USING THE ON-CHIP XDATA OF THE INFINEON C515C

Answer

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.

Copy the file STARTUP.A51 from the keilc51lib directory to your project directory.

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.
;

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

Article last edited on: 2005-07-09 12:27:37

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