68k Instruction Reference
This page documents all Motorola 68000 instructions, as well as their execution times. When instruction timings are shown, they are usually in the format of x(r/w), where x is the total number of processor cycles required for the instruction, and r/w is the total read and write cycles required for the instruction.
Instruction timings include instruction fetches, operand reads, as well as operand writes.
Contents
Address Calculation Times
It is important to remember that most instructions alter some form of memory, and thus, must calculate the address that will be accessed, which usually incurs extra processor cycles. The two columns "Byte/Word" and "Long" contain a number followed by two numbers in parenthesis. The number outside the parenthesis indicates the total number of processor cycles required, while the two numbers inside the parenthesis indicate the number of read and write cycles are required.
Timings include fetching of extension words, address computation, as well as fetching of memory operands.
| Addressing Mode | Byte/Word | Long | |
|---|---|---|---|
| Register | |||
| Dn | Data Register Direct | 0(0/0) | 0(0/0) |
| An | Address Register Direct | 0(0/0) | 0(0/0) |
| Memory | |||
| (An) | Address Register Indirect | 4(1/0) | 8(2/0) |
| (An)+ | Address Register Indirect with post-increment | 4(1/0) | 8(2/0) |
| d(An) | Address Register Indirect with displacement | 8(2/0) | 12(3/0) |
| d(An, ix) | Address Register Indirect with index | 10(2/0) | 14(3/0) |
| #xxx.W | Absolute Short | 8(2/0) | 12(3/0) |
| #xxx.L | Absolute Long | 12(3/0) | 16(4/0) |
| d(PC) | Program Counter with displacement | 8(2/0) | 12(3/0) |
| d(PC, ix) | Program Counter with index | 10(2/0) | 14(3/0) |
| #xxx | Immediate | 4(1/0) | 8(2/0) |
Move Instruction Execution Times
Note: The size of the index register (ix) does not affect the instruction execution time.
Byte and Word
| Dn | An | (An) | (An)+ | -(An) | d(An) | d(An, ix) | #xxx.W | #xxx.L | |
|---|---|---|---|---|---|---|---|---|---|
| Dn | 4(1/0) | 4(1/0) | 8(1/1) | 8(1/1) | 8(1/1) | 12(2/1) | 14(2/1) | 12(2/1) | 16(3/1) |
| An | 4(1/0) | 4(1/0) | 8(1/1) | 8(1/1) | 8(1/1) | 12(2/1) | 14(2/1) | 12(2/1) | 16(3/1) |
| (An) | 8(2/0) | 8(2/0) | 12(2/1) | 12(2/1) | 12(2/1) | 16(3/1) | 18(3/1) | 16(3/1) | 20(4/1) |
| (An)+ | 8(2/0) | 8(2/0) | 12(2/1) | 12(2/1) | 12(2/1) | 16(3/1) | 18(3/1) | 16(3/1) | 20(4/1) |
| -(An) | 10(2/0) | 10(2/0) | 14(2/1) | 14(2/1) | 14(2/1) | 18(3/1) | 20(4/1) | 18(3/1) | 22(4/1) |
| d(An) | 12(3/0) | 12(3/0) | 16(3/1) | 16(3/1) | 16(3/1) | 20(4/1) | 22(4/1) | 20(4/1) | 24(5/1) |
| d(An, ix) | 14(3/0) | 14(3/0) | 18(3/1) | 18(3/1) | 18(3/1) | 22(4/1) | 24(4/1) | 22(4/1) | 26(5/1) |
| #xxx.W | 12(3/0) | 12(3/0) | 16(3/1) | 16(3/1) | 16(3/1) | 20(4/1) | 22(4/1) | 20(4/1) | 24(5/1) |
| #xxx.L | 16(4/0) | 16(4/0) | 20(4/1) | 20(4/1) | 20(4/1) | 24(5/1) | 26(5/1) | 24(5/1) | 28(6/1) |
| d(PC) | 12(3/0) | 12(3/0) | 16(3/1) | 16(3/1) | 16(3/1) | 20(4/1) | 22(4/1) | 20(4/1) | 24(5/1) |
| d(PC, ix) | 14(3/0) | 14(3/0) | 18(3/1) | 18(3/1) | 18(3/1) | 22(4/1) | 24(4/1) | 22(4/1) | 26(5/1) |
| #xxx | 8(2/0) | 8(2/0) | 12(2/1) | 12(2/1) | 12(2/1) | 16(3/1) | 18(3/1) | 16(3/1) | 20(4/1) |
Longword
| Dn | An | (An) | (An)+ | -(An) | d(An) | d(An, ix) | #xxx.W | #xxx.L | |
|---|---|---|---|---|---|---|---|---|---|
| Dn | 4(1/0) | 4(1/0) | 12(1/2) | 12(1/2) | 12(1/2) | 16(2/2) | 18(2/2) | 16(2/2) | 20(3/2) |
| An | 4(1/0) | 4(1/0) | 12(1/2) | 12(1/2) | 12(1/2) | 16(2/2) | 18(2/2) | 16(2/2) | 20(3/2) |
| (An) | 12(3/0) | 12(3/0) | 20(3/2) | 20(3/2) | 20(3/2) | 24(4/2) | 26(4/2) | 24(4/2) | 28(5/2) |
| (An)+ | 12(3/0) | 12(3/0) | 20(3/2) | 20(3/2) | 20(3/2) | 24(4/2) | 26(4/2) | 24(4/2) | 28(5/2) |
| -(An) | 14(3/0) | 14(3/0) | 22(3/2) | 22(3/2) | 22(3/2) | 26(4/2) | 28(4/2) | 26(4/2) | 30(5/2) |
| d(An) | 16(4/0) | 16(4/0) | 24(4/2) | 24(4/2) | 24(4/2) | 28(5/2) | 30(5/2) | 28(5/2) | 32(6/2) |
| d(An, ix) | 18(4/0) | 18(4/0) | 26(4/2) | 26(4/2) | 26(4/2) | 30(5/2) | 32(5/2) | 30(5/2) | 34(6/2) |
| #xxx.W | 16(4/0) | 16(4/0) | 24(4/2) | 24(4/2) | 24(4/2) | 28(5/2) | 30(5/2) | 28(5/2) | 32(6/2) |
| #xxx.L | 20(5/0) | 20(5/0) | 28(5/2) | 28(5/2) | 28(5/2) | 32(6/2) | 34(6/2) | 32(6/2) | 36(7/2) |
| d(PC) | 16(4/0) | 16(4/0) | 24(4/2) | 24(4/2) | 24(4/2) | 28(5/2) | 30(5/2) | 28(5/2) | 32(5/2) |
| d(PC, ix) | 18(4/0) | 18(4/0) | 26(4/2) | 26(4/2) | 26(4/2) | 30(5/2) | 32(5/2) | 30(5/2) | 34(6/2) |
| #xxx | 12(3/0) | 12(3/0) | 20(3/2) | 20(3/2) | 20(3/2) | 24(4/2) | 26(4/2) | 24(4/2) | 28(5/2) |
