I'm new to assembly language, so I'm having a little trouble with my first program. I am supposed to basically recreate the following code, except in assembly language obviously. Can anyone help me fix the errors and help me get my program to work properly? I think I am close.
Original non-assembly Code:
Q = 7;
P = 15; // also test on P = 14 and P = 6
if (P > 12)
P = 8 * P + 4; // Requirement: use ASL for multiplied by 8
else
P = P - Q;
print P;
Here is what I have so far, but I'm getting errors. I'll post the errors at the bottom.
START ORG $1000 //Program starts at loc $1000
IF CMP #12,P //Is P > 12?
BLE ENDIF //If P < 12, go to ENDIF
ASL #3,P //Shift left 3 times (Multiply P * 8)
ADD #4,P //P + 4
ENDIF SUB Q,P //P - Q
* Data section
ORG $2000 //Data starts at loc 2000
P DC.W 15 //int P = 15;
Q DC.W 7 //int Q = 7;
END START
Line 4: ERROR: Invalid addressing mode Line 7: ERROR: Invalid addressing mode
I recommend that you keep the M68000 Programmer's Reference Manual around to look up the correct way of using instructions.
ASL has no #<data>,<ea> form. It does have a <ea> form, so you can do ASL P three times. Or you can move P into a register, shift it 3 bits to the left, and put the result back in P.
Likewise, there's no <ea>,<ea> form of SUB. One solution would be to move the Q into a D-register, and subtract that register from P.