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no message about A14 error generated

Oleg Sergeev

hi,

next example is compiled without errors but produces wrong results due debug.

;------------------------------------------------------------
; Test program about bug of relocatable calculations
;------------------------------------------------------------
; allocate buffer in XDATA
?XD?BUFFER	SEGMENT	XDATA
		RSEG	?XD?BUFFER
BUFFER:		DS	512	; here may be any number

;------------------------------------------------------------
; Main program
?PR?MAIN	SEGMENT CODE
		RSEG	?PR?MAIN
; load high byte of the buffer address +1 into accumulator
	MOV	A,#(HIGH(BUFFER)+1)
; !!! accumulator contains high byte without +1 !!!

	MOV	A,#(HIGH(BUFFER+256*1))
; here we obtain the correct result

	JMP	$

	END

I know source of the problem but I have no idea why no error about "INVALID RELOCATABLE EXPRESSION" is generated?

Thanks,
Oleg

Parents
  • 0 in reply to HansBernhard Broeker

    It is hard to say exactly but for lines:

    	MOV	A,#(LOW(BUFFER)+1)
	MOV	A,#(HIGH(BUFFER)+1)
	JMP	$
    final code is:
        11:         MOV     A,#(LOW(BUFFER)+1)
C:0x0000    7401     MOV      A,#0x01
    12:         MOV     A,#(HIGH(BUFFER)+1)
    13:
C:0x0002    7400     MOV      A,#0x00
    14:         JMP     $
C:0x0004    80FE     SJMP     C:0004
    Map file shows that BUFFER is located at 0x0000:
    X:0000H SYMBOL BUFFER
    So I assumed that LOW works but HIGH does not.

    Regards,
    Oleg

Reply
  • 0 in reply to HansBernhard Broeker

    It is hard to say exactly but for lines:

    	MOV	A,#(LOW(BUFFER)+1)
	MOV	A,#(HIGH(BUFFER)+1)
	JMP	$
    final code is:
        11:         MOV     A,#(LOW(BUFFER)+1)
C:0x0000    7401     MOV      A,#0x01
    12:         MOV     A,#(HIGH(BUFFER)+1)
    13:
C:0x0002    7400     MOV      A,#0x00
    14:         JMP     $
C:0x0004    80FE     SJMP     C:0004
    Map file shows that BUFFER is located at 0x0000:
    X:0000H SYMBOL BUFFER
    So I assumed that LOW works but HIGH does not.

    Regards,
    Oleg

Children
  • 0 in reply to Oleg Sergeev

    Unfortunately, HIGH and LOW are not like functions you can use in your assembler code.

    They are instead like expression-wide modifiers that change the byte the assembler/linker view for purposes of instruction construction.

    For example, all of the following expressions using HIGH are evaluated to the same result:

    high buffer + 1
1 + high buffer
high(buffer) + 1

    The reason is that when the expression is calculated, the HIGH keyword simply sets flag. The expression is calculated (ignoring the HIGH keyword). And, HIGH is applied to the result. The same is true for the LOW and other byte-specific keywords.

    So, if you want to adjust the high byte, you must do something like...

    high buffer+256

    Jon