Technical Support

C51: USING THE ON-CHIP XDATA OF THE INFINEON C515C

---

Information in this article applies to:

• C51 Version 5.50a
• C51 Version 6.03

---

QUESTION

I'm using a C515C which has 2K of on-chip XDATA from 0xF800 to 0xFFFF. I have successfully mapped my variables to this address space, but they don't seem to work. Is there something else I must do to use this memory?

ANSWER

Yes. After reset, the on-chip XRAM of the C515C is disabled. You must enable it by clearing the XMAP0 bit. This is best done in the C startup code.

1. Copy the file STARTUP.A51 from the \keil\c51\lib directory to your project directory.
2. Modify the memory initialization section of the startup code as follows:

   ;  User-defined Power-On Initialization of Memory
   ;
   ;  With the following EQU statements the initialization of memory
   ;  at processor reset can be defined:
   ;
   ;               ; the absolute start-address of IDATA memory is always 0
   IDATALEN        EQU     100H    ; the length of IDATA memory in bytes.
   ;
   XDATASTART      EQU     0F800H  ; the absolute start-address of XDATA memory
   XDATALEN        EQU     0800H   ; the length of XDATA memory in bytes.
   ;
   PDATASTART      EQU     0H      ; the absolute start-address of PDATA memory
   PDATALEN        EQU     0H      ; the length of PDATA memory in bytes.
   ;
   

3. Add the following instruction (ANL 0B1h, #01h) at the beginning of the startup code (BEFORE XDATA is cleared). If the XRAM is not enabled, it can't be cleared.

                   CSEG    AT      0
   ?C_STARTUP:     LJMP    STARTUP1
   
                   RSEG    ?C_C51STARTUP
   
   STARTUP1:
   
                   ANL     0B1h, #01h      ; CLEAR XMAP0 (enabling F800-FFFF XRAM)
   
   IF IDATALEN <> 0
                   MOV     R0,#IDATALEN - 1
                   CLR     A
   IDATALOOP:
                   MOV     @R0,A
                   DJNZ    R0,IDATALOOP
   ENDIF
   

FORUM THREADS

The following Discussion Forum threads may provide information related to this topic.

• how to enable xdata in P87C51RD+

Last Reviewed: Saturday, July 09, 2005

---

Did this article provide the answer you needed?
Yes No Not Sure