http://md.railgun.works/index.php?title=VDP&feed=atom&action=historyVDP - Revision history2024-03-29T15:37:57ZRevision history for this page on the wikiMediaWiki 1.29.0http://md.railgun.works/index.php?title=VDP&diff=1156&oldid=prevGerbilSoft: /* Calculating VRAM Addresses */ Reword2015-04-30T14:31:23Z<p><span dir="auto"><span class="autocomment">Calculating VRAM Addresses: </span> Reword</span></p>
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<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 14:31, 30 April 2015</td>
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<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>The CD bits in the command register are <del class="diffchange diffchange-inline">known as </del>the code register. They indicate if data will be read or written as well as which section of memory will be accessed. Possible values of CD include: (MSB on left)</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>The CD bits in the command register are <ins class="diffchange diffchange-inline">used to set up </ins>the code register. They indicate if data will be read or written as well as which section of memory will be accessed. Possible values of CD include: (MSB on left)</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>* CD=000000: [[VRAM]] read</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>* CD=000000: [[VRAM]] read</div></td></tr>
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</table>GerbilSofthttp://md.railgun.works/index.php?title=VDP&diff=1155&oldid=prevGerbilSoft: /* Calculating VRAM Addresses */ +8-bit VRAM read2015-04-30T14:30:48Z<p><span dir="auto"><span class="autocomment">Calculating VRAM Addresses: </span> +8-bit VRAM read</span></p>
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<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 14:30, 30 April 2015</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l952" >Line 952:</td>
<td colspan="2" class="diff-lineno">Line 952:</td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>* CD=000100: [[VSRAM]] read</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>* CD=000100: [[VSRAM]] read</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>* CD=000101: [[VSRAM]] write</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>* CD=000101: [[VSRAM]] write</div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">* CD=001100: [[VRAM]] read, 8-bit (undocumented)</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;"></ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">The 8-bit [[VRAM]] read function reads a single byte from VRAM. The returned value consists of the [[VRAM]] byte as the low byte, plus a byte from the FIFO as the high byte. It's recommended to use the standard [[VRAM]] read function instead.</ins></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>If the proper address and mode bits are set in the VDP command, a command word like this would be produced:</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>If the proper address and mode bits are set in the VDP command, a command word like this would be produced:</div></td></tr>
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</table>GerbilSofthttp://md.railgun.works/index.php?title=VDP&diff=1154&oldid=prevGerbilSoft: /* Calculating VRAM Addresses */ Improved the code register description.2015-04-30T14:27:45Z<p><span dir="auto"><span class="autocomment">Calculating VRAM Addresses: </span> Improved the code register description.</span></p>
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<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 14:27, 30 April 2015</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l843" >Line 843:</td>
<td colspan="2" class="diff-lineno">Line 843:</td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>! 16</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>! 16</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>|-</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>|-</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | <del class="diffchange diffchange-inline">M1</del></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | <ins class="diffchange diffchange-inline">CD1</ins></div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | <del class="diffchange diffchange-inline">M0</del></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | <ins class="diffchange diffchange-inline">CD0</ins></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | A13</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | A13</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | A12</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | A12</div></td></tr>
<tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l892" >Line 892:</td>
<td colspan="2" class="diff-lineno">Line 892:</td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | 0</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | 0</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>|</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>|</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | <del class="diffchange diffchange-inline">M5</del></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | <ins class="diffchange diffchange-inline">CD5</ins></div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | <del class="diffchange diffchange-inline">M4</del></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | <ins class="diffchange diffchange-inline">CD4</ins></div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | <del class="diffchange diffchange-inline">M3</del></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | <ins class="diffchange diffchange-inline">CD3</ins></div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | <del class="diffchange diffchange-inline">M2</del></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | <ins class="diffchange diffchange-inline">CD2</ins></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | 0</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | 0</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | 0</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>| align="center" | 0</div></td></tr>
<tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l944" >Line 944:</td>
<td colspan="2" class="diff-lineno">Line 944:</td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>|}</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>|}</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>The <del class="diffchange diffchange-inline">M's </del>in the command register will <del class="diffchange diffchange-inline">control the mode (</del>read<del class="diffchange diffchange-inline">/write) </del>as well as <del class="diffchange diffchange-inline">the </del>memory <del class="diffchange diffchange-inline">that </del>will be accessed. <del class="diffchange diffchange-inline">They work as following</del>:</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>The <ins class="diffchange diffchange-inline">CD bits </ins>in the command register <ins class="diffchange diffchange-inline">are known as the code register. They indicate if data </ins>will <ins class="diffchange diffchange-inline">be </ins>read <ins class="diffchange diffchange-inline">or written </ins>as well as <ins class="diffchange diffchange-inline">which section of </ins>memory will be accessed. <ins class="diffchange diffchange-inline">Possible values of CD include</ins>: <ins class="diffchange diffchange-inline">(MSB on left)</ins></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>* <del class="diffchange diffchange-inline">If M0 through M5 are 0, then </del>[[VRAM]] read <del class="diffchange diffchange-inline">mode is set.</del></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>* <ins class="diffchange diffchange-inline">CD=000000: </ins>[[VRAM]] read</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>* <del class="diffchange diffchange-inline">If M1 through M5 are 0, but M0 is 1, then </del>[[VRAM]] write <del class="diffchange diffchange-inline">mode is set.</del></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>* <ins class="diffchange diffchange-inline">CD=000001: </ins>[[VRAM]] write</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>* <del class="diffchange diffchange-inline">If M0, M1, M2, M4 and M5 are 0, but M3 is 1, then </del>CRAM read <del class="diffchange diffchange-inline">mode is set.</del></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>* <ins class="diffchange diffchange-inline">CD=001000: [[</ins>CRAM<ins class="diffchange diffchange-inline">]] </ins>read</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>* <del class="diffchange diffchange-inline">If M2 through M5 are 0, but M0 and M1 are 1, then </del>CRAM write <del class="diffchange diffchange-inline">mode is set.</del></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>* <ins class="diffchange diffchange-inline">CD=000011: [[</ins>CRAM<ins class="diffchange diffchange-inline">]] </ins>write</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>* <del class="diffchange diffchange-inline">If M0, M1, M3, M4 and M5 are 0, but M2 is 1, then </del>VSRAM read <del class="diffchange diffchange-inline">mode is set.</del></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>* <ins class="diffchange diffchange-inline">CD=000100: [[</ins>VSRAM<ins class="diffchange diffchange-inline">]] </ins>read</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>* <del class="diffchange diffchange-inline">If M1, M3, M4 and M5 are 0, but M0 and M2 are 1, then </del>VSRAM write <del class="diffchange diffchange-inline">mode is set.</del></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>* <ins class="diffchange diffchange-inline">CD=000101: [[</ins>VSRAM<ins class="diffchange diffchange-inline">]] </ins>write</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>If the proper address and mode bits are set in the VDP command, a command word like this would be produced:</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>If the proper address and mode bits are set in the VDP command, a command word like this would be produced:</div></td></tr>
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</table>GerbilSofthttp://md.railgun.works/index.php?title=VDP&diff=1152&oldid=prevLazzie: /* DMA Limitations */ Added DMA Copy issue notes2015-04-16T07:51:58Z<p><span dir="auto"><span class="autocomment">DMA Limitations: </span> Added DMA Copy issue notes</span></p>
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<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 07:51, 16 April 2015</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l1180" >Line 1,180:</td>
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<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>A similar issue occurs if the second word of the DMA address is written to the mirror of the VDP port (at $C00006) which may cause the first word of the DMA transfer to not be transferred. This can be circumvented easily by writing the second word of the transfer address to the first control port, not the mirror of it. A similar problem can occur when performing a DMA transfer from the [[Mega CD]] Word RAM, due to a timing problem with the DRAM that prevents the address from getting latched into the memory, although all following words that will be transferred correctly. To circumvent this problem, set the DMA source and destination as one word less than needed, and length one more than is needed. This may corrupt the word in VRAM before, but ensure all data will be transferred correctly.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>A similar issue occurs if the second word of the DMA address is written to the mirror of the VDP port (at $C00006) which may cause the first word of the DMA transfer to not be transferred. This can be circumvented easily by writing the second word of the transfer address to the first control port, not the mirror of it. A similar problem can occur when performing a DMA transfer from the [[Mega CD]] Word RAM, due to a timing problem with the DRAM that prevents the address from getting latched into the memory, although all following words that will be transferred correctly. To circumvent this problem, set the DMA source and destination as one word less than needed, and length one more than is needed. This may corrupt the word in VRAM before, but ensure all data will be transferred correctly.</div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;"></ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">DMA copies do not work well when copying data to and from the sprite table. While all data is properly copied, the sprite cache is not completely updated, causing various visual issues including disappearing sprites.</ins></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>There is significantly less DMA bandwidth available on NTSC-60 hardware than there is on PAL-50 hardware, due to the fact that NTSC hardware has a higher output framerate.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>There is significantly less DMA bandwidth available on NTSC-60 hardware than there is on PAL-50 hardware, due to the fact that NTSC hardware has a higher output framerate.</div></td></tr>
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</table>Lazziehttp://md.railgun.works/index.php?title=VDP&diff=1104&oldid=prevGerbilSoft: /* $15 to $17 - DMA Source */ >divided by zero2015-03-18T17:01:04Z<p><span dir="auto"><span class="autocomment">$15 to $17 - DMA Source: </span> >divided by zero</span></p>
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<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 17:01, 18 March 2015</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l748" >Line 748:</td>
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<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>* H5-H0 is the high byte of the DMA source address. If DMD1=0, DMD0 acts as H6.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>* H5-H0 is the high byte of the DMA source address. If DMD1=0, DMD0 acts as H6.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>* DMD1-DMD0 tell the VDP what type of DMA shall be coming up:</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>* DMD1-DMD0 tell the VDP what type of DMA shall be coming up:</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>** 0x: VDP will copy data at the specified M68K source address to the destination target specified in the command word. Only DMD1 is significant here; DMD0 becomes the high bit of the source address. (Note that in this mode, the source address is divided by <del class="diffchange diffchange-inline">zero</del>; DMA source of $7F0000 corresponds to M68K address $FE0000.)</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>** 0x: VDP will copy data at the specified M68K source address to the destination target specified in the command word. Only DMD1 is significant here; DMD0 becomes the high bit of the source address. (Note that in this mode, the source address is divided by <ins class="diffchange diffchange-inline">two</ins>; DMA source of $7F0000 corresponds to M68K address $FE0000.)</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>** 10: DMA FILL. VDP will fill the specified destination address with the next word written to the data port.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>** 10: DMA FILL. VDP will fill the specified destination address with the next word written to the data port.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>** 11: DMA COPY. VDP will copy a block of VRAM from the source address to the destination address.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>** 11: DMA COPY. VDP will copy a block of VRAM from the source address to the destination address.</div></td></tr>
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</table>GerbilSofthttp://md.railgun.works/index.php?title=VDP&diff=1092&oldid=prevGerbilSoft: /* Nametables */2015-03-16T19:29:27Z<p><span dir="auto"><span class="autocomment">Nametables</span></span></p>
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<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 19:29, 16 March 2015</td>
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<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>When the priority bit is set, the tile will be displayed above low priority tiles on the same plane, or planes 'below' it in the [[#Priority|priority ordering<del class="diffchange diffchange-inline">.</del>]] Horizontal and Vertical flip will flip the tile either horizontally or vertically. The palette bits allow displaying the tile with one of the four palette lines. It is worth noting that when Interlace mode 2 is selected, the LSB of the tile index will be ignored, as tiles are now 8x16 in size.</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>When the priority bit is set, the tile will be displayed above low priority tiles on the same plane, or planes 'below' it in the [[#Priority|priority ordering]]<ins class="diffchange diffchange-inline">. </ins>Horizontal and Vertical flip will flip the tile either horizontally or vertically. The palette bits allow displaying the tile with one of the four palette lines. It is worth noting that when Interlace mode 2 is selected, the LSB of the tile index will be ignored, as tiles are now 8x16 in size.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>=== Priority ===</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>=== Priority ===</div></td></tr>
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</table>GerbilSofthttp://md.railgun.works/index.php?title=VDP&diff=1091&oldid=prevGerbilSoft: /* Horizontal Interrupt */ Fix register links.2015-03-16T19:29:01Z<p><span dir="auto"><span class="autocomment">Horizontal Interrupt: </span> Fix register links.</span></p>
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<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>==== Horizontal Interrupt ====</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>==== Horizontal Interrupt ====</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>The horizontal interrupt is fired once the VDP has completed outputting the scanline specified by the [[<del class="diffchange diffchange-inline">VDP</del>#<del class="diffchange diffchange-inline">Register_10</del>|Register 10<del class="diffchange diffchange-inline">.</del>]] The VDP's internal scanline counter is loaded with the value from this register at the top of the screen, and once it hits 0, the interrupt will be fired and the register re-loaded with the value. For example, if the register were to be set to $10, the interrupt would be fired every 16 scanlines. Horizontal interrupts have an interrupt level of 4, meaning it can interrupt a VBlank.</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>The horizontal interrupt is fired once the VDP has completed outputting the scanline specified by the [[#<ins class="diffchange diffchange-inline">$0A - Horizontal Interrupt Counter</ins>|Register 10]]<ins class="diffchange diffchange-inline">. </ins>The VDP's internal scanline counter is loaded with the value from this register at the top of the screen, and once it hits 0, the interrupt will be fired and the register re-loaded with the value. For example, if the register were to be set to $10, the interrupt would be fired every 16 scanlines. Horizontal interrupts have an interrupt level of 4, meaning it can interrupt a VBlank.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Due to how the VDP is designed, there is a delay before the new value set in [[#<del class="diffchange diffchange-inline">Register 10</del>|Register 10]] becomes effective. The counter for the horizontal interrupt must first expire with the previous value before the new one takes effect. For example, when it it is set to $10, and after the first interrupt on line $10 it is set to $08, the next interrupt will still happen after $10 scanlines, at which point the new value will take effect. This is caused because the VDP's internal scanline counter for horizontal interrupts is only reloaded with the value of [[#Register <del class="diffchange diffchange-inline">10|register </del>10]] once it reaches 0, not when the register is written to.</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Due to how the VDP is designed, there is a delay before the new value set in [[#<ins class="diffchange diffchange-inline">$0A - Horizontal Interrupt Counter</ins>|Register 10]] becomes effective. The counter for the horizontal interrupt must first expire with the previous value before the new one takes effect. For example, when it it is set to $10, and after the first interrupt on line $10 it is set to $08, the next interrupt will still happen after $10 scanlines, at which point the new value will take effect. This is caused because the VDP's internal scanline counter for horizontal interrupts is only reloaded with the value of [[#<ins class="diffchange diffchange-inline">$0A - Horizontal Interrupt Counter|</ins>Register 10]] once it reaches 0, not when the register is written to.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>==== External Interrupt ====</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>==== External Interrupt ====</div></td></tr>
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</table>GerbilSofthttp://md.railgun.works/index.php?title=VDP&diff=1090&oldid=prevGerbilSoft: /* VDP I/O Layout */ Fix register link.2015-03-16T19:27:37Z<p><span dir="auto"><span class="autocomment">VDP I/O Layout: </span> Fix register link.</span></p>
<table class="diff diff-contentalign-left" data-mw="interface">
<col class='diff-marker' />
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<col class='diff-marker' />
<col class='diff-content' />
<tr style='vertical-align: top;' lang='en-GB'>
<td colspan='2' style="background-color: white; color:black; text-align: center;">← Older revision</td>
<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 19:27, 16 March 2015</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l56" >Line 56:</td>
<td colspan="2" class="diff-lineno">Line 56:</td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>|}</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>|}</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Most of the time, it is not required to use any memory addresses besides the control and data ports. Note that the data and control ports are really only a word wide, but they are mirrored. Due to the way how the 16 bit 68000 does longword accesses (write high word, increment address, write low word,) this allows for more efficient longword writes, than two word writes to the same address. The H/V counter is usually not used for any significant purposes outside of randomisation and light guns. To use the H/V counter, it must be enabled in [[#Register <del class="diffchange diffchange-inline">00</del>|Register 0.]] Followed after the H/V counter is the [[PSG]] register, which can only be accessed as a byte on the odd addresses. It can also be accessed by the Z80, so accesses between the [[PSG]] register must be coordinated if both the Z80 and 68000 are going to be accessing it. Lastly, there is a 'debug register' which was presumably used during VDP development to test various features and verify functionality. Not much is known about it, besides what is [[#Debug_Register|noted below.]]</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Most of the time, it is not required to use any memory addresses besides the control and data ports. Note that the data and control ports are really only a word wide, but they are mirrored. Due to the way how the 16 bit 68000 does longword accesses (write high word, increment address, write low word,) this allows for more efficient longword writes, than two word writes to the same address. The H/V counter is usually not used for any significant purposes outside of randomisation and light guns. To use the H/V counter, it must be enabled in [[#<ins class="diffchange diffchange-inline">$00 - Mode </ins>Register <ins class="diffchange diffchange-inline">1</ins>|Register 0.]] Followed after the H/V counter is the [[PSG]] register, which can only be accessed as a byte on the odd addresses. It can also be accessed by the Z80, so accesses between the [[PSG]] register must be coordinated if both the Z80 and 68000 are going to be accessing it. Lastly, there is a 'debug register' which was presumably used during VDP development to test various features and verify functionality. Not much is known about it, besides what is [[#Debug_Register|noted below.]]</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>Due to the way the Mega Drive was designed, the 64 KB of [[VRAM]] were not mapped to [[Motorola 68000|M68k]] address space, which opens up lots of more space for I/O peripherals and other devices but can create an inconvenience in programming the VDP.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>Due to the way the Mega Drive was designed, the 64 KB of [[VRAM]] were not mapped to [[Motorola 68000|M68k]] address space, which opens up lots of more space for I/O peripherals and other devices but can create an inconvenience in programming the VDP.</div></td></tr>
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</table>GerbilSofthttp://md.railgun.works/index.php?title=VDP&diff=1089&oldid=prevGerbilSoft: /* Vertical Scrolling */ Fix register link.2015-03-16T19:26:52Z<p><span dir="auto"><span class="autocomment">Vertical Scrolling: </span> Fix register link.</span></p>
<table class="diff diff-contentalign-left" data-mw="interface">
<col class='diff-marker' />
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<col class='diff-marker' />
<col class='diff-content' />
<tr style='vertical-align: top;' lang='en-GB'>
<td colspan='2' style="background-color: white; color:black; text-align: center;">← Older revision</td>
<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 19:26, 16 March 2015</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l1578" >Line 1,578:</td>
<td colspan="2" class="diff-lineno">Line 1,578:</td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>=== Vertical Scrolling ===  </div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>=== Vertical Scrolling ===  </div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Like [[#Horizontal_Scrolling|Horizontal Scrolling,]] Vertical Scrolling allows scrolling of the content on the VDP's 2 planes, but vertically. The setup of VScroll is decided by [[#<del class="diffchange diffchange-inline">Register_11</del>|Register 11.]] Both planes can be scrolled completely, or the VDP can scroll a 2 tile wide column of the name tables at once. Vertical Scrolling data is located in RAM on the VDP itself. It is also written like regular [[VRAM<del class="diffchange diffchange-inline">|VRAM,</del>]] but it is not exactly fast either, so a buffer should be applied here too.</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Like [[#Horizontal_Scrolling|Horizontal Scrolling,]] Vertical Scrolling allows scrolling of the content on the VDP's 2 planes, but vertically. The setup of VScroll is decided by [[#<ins class="diffchange diffchange-inline">$0B - Mode Register 3</ins>|Register 11.]] Both planes can be scrolled completely, or the VDP can scroll a 2 tile wide column of the name tables at once. Vertical Scrolling data is located in RAM on the VDP itself. It is also written like regular [[VRAM]]<ins class="diffchange diffchange-inline">, </ins>but it is not exactly fast either, so a buffer should be applied here too.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>* The first mode of vertical scrolling is much like the first mode of horizontal scrolling - the entire screen is scrolled vertically by the first long in VSRAM. The first word scrolls the FG, and the second scrolls the BG.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>* The first mode of vertical scrolling is much like the first mode of horizontal scrolling - the entire screen is scrolled vertically by the first long in VSRAM. The first word scrolls the FG, and the second scrolls the BG.</div></td></tr>
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</table>GerbilSofthttp://md.railgun.works/index.php?title=VDP&diff=1088&oldid=prevGerbilSoft: /* Horizontal Scrolling */ Comma.2015-03-16T19:26:31Z<p><span dir="auto"><span class="autocomment">Horizontal Scrolling: </span> Comma.</span></p>
<table class="diff diff-contentalign-left" data-mw="interface">
<col class='diff-marker' />
<col class='diff-content' />
<col class='diff-marker' />
<col class='diff-content' />
<tr style='vertical-align: top;' lang='en-GB'>
<td colspan='2' style="background-color: white; color:black; text-align: center;">← Older revision</td>
<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 19:26, 16 March 2015</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l1573" >Line 1,573:</td>
<td colspan="2" class="diff-lineno">Line 1,573:</td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>*If whole plane scrolling is enabled, the VDP high word will scroll the FG plane, and the low plane will scroll the BG plane. Note that the plane will wrap once it reaches the edge of the plane's size.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>*If whole plane scrolling is enabled, the VDP high word will scroll the FG plane, and the low plane will scroll the BG plane. Note that the plane will wrap once it reaches the edge of the plane's size.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>*When per-row horizontal scrolling is enabled, every longword in the HScroll table will tell the VDP how much to scroll every 8-pixel row on-screen. The format is still the same as before - first word scrolls the FG, and the second scrolls the BG.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>*When per-row horizontal scrolling is enabled, every longword in the HScroll table will tell the VDP how much to scroll every 8-pixel row on-screen. The format is still the same as before - first word scrolls the FG, and the second scrolls the BG.</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>*Lastly is per-scanline horizontal scrolling. This mode allows scrolling of all 224 on-screen scanlines (240 in PAL mode) individually. This can be used to create visually appealing effects such as water wobbles, and so on. Each long in the HScroll table will tell the VDP how to scroll each scanline. As previously, the first word will be controlling controlling the FG, and the second controlling the BG. This mode also takes up the most space in [[VRAM<del class="diffchange diffchange-inline">|VRAM,</del>]] with 960 bytes.  </div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>*Lastly is per-scanline horizontal scrolling. This mode allows scrolling of all 224 on-screen scanlines (240 in PAL mode) individually. This can be used to create visually appealing effects such as water wobbles, and so on. Each long in the HScroll table will tell the VDP how to scroll each scanline. As previously, the first word will be controlling controlling the FG, and the second controlling the BG. This mode also takes up the most space in [[VRAM]]<ins class="diffchange diffchange-inline">, </ins>with 960 bytes.  </div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>It's best to have an in-RAM buffer for the last two modes as writing to the VDP isn't exactly fast. The buffer can then be transferred using DMA every VBlank.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>It's best to have an in-RAM buffer for the last two modes as writing to the VDP isn't exactly fast. The buffer can then be transferred using DMA every VBlank.</div></td></tr>
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</table>GerbilSoft