A51: CONVERTING LEGACY 8051 ASSEMBLY CODE TO KEIL C51/A51

Information in this article applies to:

• C51 All Versions

QUESTION

How do I convert my legacy code written for another assembler into Keil A51 assembly code ?

ANSWER

Keil gives a handy template found at C:\Keil\C51\ASM\Template.A51. So open a UV2 project and then choose View> Workbook mode. Then File>open> Browse C:\Keil\C51\asm\Template.a51 Then open your assembly file legacy.a51 Then Windows>title Vertically. template.a51 and the Legacy .a51 side by side . This view enables you to look at the template and change any of legacy .A51 to conform with the Keil A51 assembler. As always use the book feature to open the keil documentation to the Keil A51 Assembler and Utililites to look up specific directives and to see the Template.A51 example in full detail. The example below is just for illustration on differences you may find.

1) Add   $NOMOD51                ; disable predefined 8051 registers
            #include <reg52.h>      // include CPU definition file (for example, 8052)
2) Comment out any TiTle Directive
3) Comment Out any $PAGELENGTH(58)
                          any $PAGEWIDTH(88)
                          any $XREF NOGEN
                          any $SYMBOLS
µVision will set these parameters Project>options "Target 1"> Listings>

4) Make Sure that the  Public and External areas are properly sequenced.


5) Add  ?STACK          SEGMENT IDATA           ; ?STACK goes into IDATA RAM.
                                   RSEG    ?STACK          ; switch to ?STACK segment.
                                   DS      5                       ; reserve your stack space
                                                                       ; 5 bytes in this example.
Between new public area and segment declaration areas.   This will put the STACK segment in the main module.

6) Then ensure that the main module is correctly vectored for reset

; Provide an LJMP to start at the reset address (address 0) in the main module.
; You may use this style for interrupt service routines.
;------------------------------------------------------------------------------
                CSEG    AT      0       ; absolute Segment at Address 0
                LJMP    start           ; reset location (jump to start)


7)  Then ensure Code Segment reservation


;------------------------------------------------------------------------------
; CODE SEGMENT--Reserves space in CODE ROM for assembler instructions.
;------------------------------------------------------------------------------
code_seg_name   SEGMENT CODE

                RSEG    code_seg_name   ; switch to this code segment

                USING   0               ; state register_bank used
                                        ; for the following program code.

start:          MOV     SP,#?STACK-1    ; assign stack at beginning

;------------------------------------------------------------------------------

; INSERT YOUR ASSEMBLY PROGRAM HERE
This will be copied from your legacy.a51

8) Then after all the  legacy.a51 assembly code routines add any Intterupt service routines.
   an example the following ISR's.


;------------------------------------------------------------------------------
; To include an interrupt service routins, provide an LJMP to the ISR at the
; interrupt vector address.
;------------------------------------------------------------------------------
                CSEG    AT  0BH         ; 0BH is address for Timer 0 interrupt
                LJMP    timer0int

;------------------------------------------------------------------------------
; Give each interrupt function its own code segment.
;------------------------------------------------------------------------------
int0_code_seg   SEGMENT CODE            ; segment for interrupt function
                RSEG    int0_code_seg   ; switch to this code segment
                USING   1               ; register bank for interrupt routine

timer0int:      PUSH    PSW
                MOV     PSW,#08H        ; register bank 1
                PUSH    ACC
                MOV     R1,data_variable
                MOV     DPTR,#xdata_variable
                MOVX    A,@DPTR
                ADD     A,R1
                MOV     data_variable1,A
                CLR     A
                ADD     A,#0
                MOV     data_variable1+1,A
                POP     ACC
                POP     PSW
                RETI


9) Then as always ensure that the END directive is used

;------------------------------------------------------------------------------
; The END directive is ALWAYS required.
;------------------------------------------------------------------------------
                END             ; End Of File

FORUM THREADS

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Last Reviewed: Thursday, September 22, 2005