Assembler: please kick me in the right direction

[Demon]

Ok, I've researched each instruction and these 5 have no direct translations:

PUSH, push direct byte onto stack
POP, pop direct byte from stack
MUL, multiply
ADDC, add into accumulator
MOVC, move code byte to accumulator

I wouldn't be surprised if the equivalent PIC Macro instructions are staring me in the face, but I don't want to start guessing. Here is some code to show the context the commands are used in:

; write an ASCII character to the display
; The font file starts at ascii 32 (blank). The default font is 8x8 pixels
; INPUTS - character in register A
write_char:
push dph
push dpl
clr c
subb a,#32 ;ascii font with blank
mov b,#8 ;multiply by 8 (8 bytes/char)
mul ab
add a,#low(font) ;add to font table address
mov dpl,a
mov a,b
addc a,#high(font)
mov dph,a
mov r0,#8 ;8 bytes/char
wbyte: clr a
movc a,@a+dptr
acall write_data
inc dptr
djnz r0,wbyte
pop dpl
pop dph
ret

8051 assembler reference here:
http://www.ece.umr.edu/computing/uni...e/tasking/asm/

PIC Macro assembler reference:

Robert

[Darrel Taylor]

Robert,

The PUSH and POP were apparently used to save 2 variables that were used in the write_char: routine. You can just use separate variables to temporarily store the two bytes, instead of trying to use the stack.

MUL can be replaced with the MUL?BBB or MUL?BBW macro.

For the addc and movc, you can either manipulate the EEADDR, EECON and EEDATA registers manually, or you could break out of ASM and use the READCODE statement to get the byte first, then do the ADDWF or MOVWF.

HTH,
Darrel

[Demon]

Like this?


dph data 42h <--- add this line with existing DATA statement
dpl data 43h <--- add this line with existing DATA statement


write_char:
push dph <--- delete this line
push dpl <--- delete this line
...
mov dpl,a
...
mov dph,a
...
pop dpl <--- delete this line
pop dph <--- delete this line
ret

Robert

[Demon]

"MUL can be replaced with the MUL?BBB or MUL?BBW macro."

Darrel, can you point me to some reference on macros? I Googled but did not find anything relevant (that I could see).

The MeLabs PM manual didn't have any mention for 'mul' or 'bbb'.

Robert

[Darrel Taylor]

I was thinking something more like this...

dph_save VAR BYTE
dpl_save  VAR BYTE

ASM
write_char:
    MOVE?BB  dph, _dph_save
    MOVE?BB  dpl, _dpl_save

    push dph <--- delete this line
    push dpl <--- delete this line
...

...
    pop dpl <--- delete this line
    pop dph <--- delete this line

    MOVE?BB  _dph_save, dph 
    MOVE?BB  _dpl_save, dpl 
return

...

ENDASM

And, here's a little more info on the MOVE macro's
http://www.picbasic.co.uk/forum/showthread.php?p=2009

.

[Demon]

What type of variables are the variables a, b and c considered? My first quess would have been a work register, but I'd like to be sure.

Since there are only 2 variables in the equation, the new command should be MUL?xx, right?

(available letters seen in your reply to PIC Beginner in other thread)

Robert

[Darrel Taylor]

This page describes the 8051 registers, but the whole site is pretty good too.
http://www.8052.com/tutbregs.phtml#R%20Registers

The MUL?xxx macro usually has 3 paramaters, the third one is the result of multiplying the first two.

For instance, if you had the following variables ...

A  VAR  BYTE
B  VAR  BYTE
Y  VAR  BYTE
Z  VAR  WORD

THEN ...

  this ASM macro              is same as this PBP statement
  ---------------------       -------------------------
    MUL?BBB   _A, _B, _Y          Y = A * B
    MUL?BBW   _A, _B, _Z          Z = A * B
    MUL?BWW   _A, _Z, _Z          Z = A * Z

And, you can see that often it's easier to just jump out of ASM and handle it in Basic.

------------------
If you do use the MUL? macros, there's something else you have to do to get them to work. Since, they are from the PBPPIC14.MAC file, they don't automaticaly get included with the project. So you have to Trick PBP into thinking it needs those macros.

This bit of code doesn't use any Program space since the ifdef keeps it from being compiled. But PBP sees the statements and includes any macros that are associated with them.

@  ifdef DoNotCompile                        ' Macro to include
       R0.LowByte = R0.LowByte * R0.LowByte  ' MUL?BBB
       R0 = R0.LowByte * R0.LowByte          ' MUL?BBW
       R0 = R0.LowByte * R0                  ' MUL?BWW
@  endif

But then, If you do it in Basic, you don't have to worry about it.

Merry X-Mas,
Darrel

[Demon]

I'm going with basic for the multiplication. Only problem is that table 4.1 in this document is confusing:
http://xess.com/manuals/asm51.pdf

The entry for MUL is:

B x A --> B,A

Ok, so what does that mean? The result is placed in both A and B? In addition, the result is accumulated in the first variable. I expected something similar, either in the first, or in the second, but not both. Obviously I'm misunderstanding something here.

I tried finding Note 7, but I can't see it anywhere.

Robert