ASM 86 LESSON 5

LESSON5:

If.. Then.. Elsestatements allow the program to branch off in many different directions. ASM does not support these staments directly, but using CP along with JR/JPyou can acheive the effect.

Theseare the instructions/ideas that will be covered in this lesson: CALL RET FUNCTIONS

CALL
Call allowsyou to jump to a different location in the ASM program, while saving whereit was, so it can return to that location later. (see also ret)

CALL cc,LABEL (where cc=c,nc,z,nz,p,m,pe,orpo)

If the condition cc is true then it jumps to the label. CC is OPTIONAL.

call _clrLCD ; calls the ROMfunction to clear the LCD
call z,_clrLCD ; only calls the function if the Zeroflag is set

back to list of instructions

RET
RET, returnspower back to where the last CALL statement was made,or back the TI/OS-SHELL, if no CALLs where made. It's actually similiarto the stack, but it's easier to explain it this way.

RET cc (where cc=c,nc,z,nz,p,m,pe,or po)

If cc is true then the ret is executed. CC isOPTIONAL

back to list of instructions

FUNCTIONS
Putting theCALL and RET commands together you are given a powerful way to modulateyour programs. You can create functions that perform certain tasks,and even accept input and produce output.

ld a,5
call Add3 ; calls our function Add3which adds 3 to the reg. A
            ; and stores the new value in B
            ;NOW b=a+3, or 8
ld c,b     ;c=b, c=8
:
.
Add3:
ld b,a     ;b=a
inc b      ;
inc b      ;
inc b      ;b=a+3
ret       ;returns control to next line after CALL was made.

back to list of instructions

LESSON4 INDEX This is the end of the lesson, I do not gaurantee any correctnessof any statements made above.