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DATA to XDATA issue

REY Stephane

Hi people,

I've some troubles with some variables declaration.
I'm using the old Keil compîler C51 V5.50.

When writing :

U8 u8CommandIndex=0;
with U8 = unsigned char, it's ok.

Now I want to relocate the variable into the XDATA segment. The declaration becomes :
xdata U8 u8CommandIndex=0;
But in this case, my variable isn't initialized to 0. The value is the last one before the reset.

Why the initialization isn't done in this case ?

Regards
Stephane

Parents
  • 0 in reply to Jon Ward

    yes, I've set the end of XDATA as follow :

    XDATALEN	EQU	0F00H	; the length of XDATA memory in bytes.
				; 8Kb = 1F00H
				; 4Kb = 0F00H

    I'm using p89c664 with 4K of internal RAM.

    I don't understand how it's possible to have some variable keeping their last value if the XDATA RAM is cleared by Startup.a51 code as follow :
    IF XDATALEN <> 0
		MOV	DPTR,#XDATASTART
		MOV	R7,#LOW (XDATALEN)
  IF (LOW (XDATALEN)) <> 0
		MOV	R6,#(HIGH XDATALEN) +1
  ELSE
		MOV	R6,#HIGH (XDATALEN)
  ENDIF
		CLR	A
XDATALOOP:	MOVX	@DPTR,A
		INC	DPTR
		DJNZ	R7,XDATALOOP
		DJNZ	R6,XDATALOOP
ENDIF

    Moreover, in my code, why it's not initialized in XDATA when writting what I've described in myprevious post.


    Stephane

Reply
  • 0 in reply to Jon Ward

    yes, I've set the end of XDATA as follow :

    XDATALEN	EQU	0F00H	; the length of XDATA memory in bytes.
				; 8Kb = 1F00H
				; 4Kb = 0F00H

    I'm using p89c664 with 4K of internal RAM.

    I don't understand how it's possible to have some variable keeping their last value if the XDATA RAM is cleared by Startup.a51 code as follow :
    IF XDATALEN <> 0
		MOV	DPTR,#XDATASTART
		MOV	R7,#LOW (XDATALEN)
  IF (LOW (XDATALEN)) <> 0
		MOV	R6,#(HIGH XDATALEN) +1
  ELSE
		MOV	R6,#HIGH (XDATALEN)
  ENDIF
		CLR	A
XDATALOOP:	MOVX	@DPTR,A
		INC	DPTR
		DJNZ	R7,XDATALOOP
		DJNZ	R6,XDATALOOP
ENDIF

    Moreover, in my code, why it's not initialized in XDATA when writting what I've described in myprevious post.


    Stephane

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