How to use xdata?

try some readable code, once I found Index was not index, I gave up.

I know that some belong to a club with the motto "If C is readable, it is not true C", please resign your membership and post again.

Erik

Hsu,

I think people are having a hard time understanding your question. It looks like you are attempting to write a routine to initialize your xdata space. It looks like you want a function that will take a value passed in, and then write that value to every location in xdata. For instance, you want the call:

Clear_DDRam(0x00)

void Fill_DDRAM(unsigned char value);

void main(void) {
   Fill_DDRAM(0x00);
   while(1);
}

void Fill_DDRAM(unsigned char value) {
   unsigned char xdata * data Index;
   int data loopcount;
   Index = 0x0000;
   P3_1 = 0;
   P3_0 = 0;
   P1_0 = 0;
   for (loopcount = 0; loopcount < 65535; loopcount++) {
      P3_4 = 0;
      *Index = value;
      P3_4 = 1;
      Index++;
   }
   *Index = value;  //Take care of last location
}

Hi,

Assuming that the above interpretation(s) is/are correct and all that is required is to fill an area of xram all with the same value, can't the library function memset be used to fill it?

Mark.

Hi Everyone
I post my assembler code and use a illustration says what it is meant to say and
hope you can clearly understand my questions?

Assembler code
;------------------------------
DDRAM_RESET:
MOV DPTR,#0000H
MOV R0,#00H
MOV R1,#00H
MOV A,#00H
RESET1: ;reset from 0000h to FF00h
CALL ZEROWR
INC DPTR
INC R0
CJNE R0,#00H,RESET1
INC R1
CJNE R1,#FFH,RESET1

RESET2: ;reset 00FFh more
CALL ZEROWR
INC DPTR
INC R0
CJNE R0,#FFH,RESET2

RET
;--------------------------------------------ZEROWR: ;Write 00 to MEM(DDRAM) thru 1352
CLR P3.4 ;MEMCS#=0,
CLR P3.1
CLR P3.0
CLR P1.0 ;Ereset=0;
MOVX @DPTR,A
SETB P3.4 ;MEMCS#=1
RET
;------------------------------------------
Illustration:

The data(index)=0x00
__
|00|Index(Address 0) | Next address
|__| V
|00|Index(address 1)
|__|
. .
. .
__
|00|Index(Address 65534) | Next address
|__| V
|00|Index(address 65535)
|__|

The external of memory start address(Index)=0x00
The next address(Index+1)=0x01

My guess it

char xdata *xPtr;

xPtr = 0;
*xPtr = 0;

Mark,

Sure, but I don't know if this is just a learning sort of test case for him and he wants to actually do something else in practice. For instance, maybe he wants to change the function to write a pattern to memory or something. Who knows?

Hsu,

That's what my code does. Also, you should not be calling the variable that holds your data "index." Aside from the fact that you already have a variable called "Index" and this is confusing, the "index" variable isn't being used as an index. Just take a look at the code I posted, and see if it's not what you're doing.

Also, you use a CLR operation on P3.1, P3.0, and P1.0 INSIDE your loop, but nothing ever sets these high. You should put these up at the start of DDRAM_RESET for efficiency.

Dear Jay

Thanks for your suggest code that I've tried and modify for my application. It is OK.