I've been doing some extra homework from my textbook to prepare for my 68000 Assembly exam coming up in the next few weeks. There are currently 4 questions which ask how the user mode can be started while already being executed in supervisor mode. I know that the instructions EOR, ANDI, and MOVE will let me do this, but I was wondering if the following examples are valid to start user mode:
EOR D0,SR ;SR is status register (is this the right way to address the SR?)
ANDI #1,SR ;Starting user via ANDI
MOVEI, #1,SR ;Starting user via MOVEI
Are the above three instructions valid to start the user mode while already in supervisor mode?
My final question has to do with the trace mode. I am completely lost with this one and I need a little guidance. Here is the question:
Illustrate how a user program at address $4000 can be started in trace mode with an interrupt mask level of 5.
If I could get any tips I would very much appreciate it. Thank you!
Oh, the good old days of 68000 programming. I remember typing move.w #$2700,sr like it was yesterday.
You are on the right track. EORI, ANDI, and MOVEI can all modify the status register. Your attempt to use the immediate value #1 is wrong, however.
One of these ought to work:
eori #$2000,sr
andi #$dfff,sr
move #$2000,sr ;Depends on what interrupt level you want.
As for the second part of your question, a hint is:
move #$8500,sr