68k register addresses

Question

This question is begging for a bunch of "why are you doing this?" responses.

I haven't been able to find this information in the 68k Programmer's Reference Manual , but that may be because I'm not sure of what verbiage to search for.

Here is the instruction format for the 68k's ADD opcode.

Bits 0-2 and 9-11 designate registers. What are the binary representations of the 68k's registers? Are they "addresses"?

Yes, I am aware that I can write a 68k assembly program and debug it to find this information. I'm looking for a reference. Thanks!

Answer 1

See Sec. 2.1, "Instruction Format":

An instruction specifies the function to be performed with an operation code and defines the location of every operand. Instructions specify an operand location by register specification, the instruction's register field holds the register's number ; by effective address, the instruction's effective address field contains addressing mode information; or by implicit reference, the definition of the instruction implies the use of specific registers. (emphasis added)

Answer 2

These probably refer to the An and Dn registers listed in figure 1-1, page 1-2 of the manual you linked.

Answer 3

The 3 bits specify the address register number, from 0 (bits: 0-0-0) to 7 (bits: 1-1-1). But generally you can let the assembler worry about this stuff. I hope this helps, Dave