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Declare assembler variable for C source file

JBaben

Hello,

how to declare the register R1 in my assembly code to R1 in the C source file to be able to use:

C-Program

extern void key_board(void);

extern unsigned char R1;     // ?

main {

....

 if (R1 == 0x03) { ….. } 

....

}

Assembler-Code

NAME	KEY_BOARD

TASTEN_PORT     EQU P1             ; benuetzter PORT
P_ANZ           EQU  03H           ; Anzahl Portleitungen
;TASTATUR_MODUS  BIT  [0]          ; Steuerbit fuer Modus (20.0)
EINGAENGE       EQU  00010111B     ; Maske fuer Tastaturport:
								   ; Tastaturpins = 1
								  ; unbenuetzte Portpins:
								  ; Eingaenge : 1
								  ; Ausgaenge : 0
TASTEN_NUMMER   EQU  01H          ; Register 1
SPALTEN_ZAEHLER EQU  02H          ;          2
ZEILEN_ZAEHLER  EQU  03H          ;          3
AUSGABE_MASKE   EQU  04H          ;          4
EINLESE_MASKE   EQU  05H          ;          5

ZAHLEN          EQU    00H
FERTIG          EQU    03H
LOESCHEN        EQU    05H
	

?PR?key_board?KEY_BOARD    SEGMENT CODE
	EXTRN	CODE (c_func)
	EXTRN   CODE (key_input)
	PUBLIC	key_board

	RSEG  ?PR?key_board?KEY_BOARD
key_board:
;****************************************************************
TASTATUR:
	 MOV   A,TASTEN_PORT      ; Pruefen, ob Taste noch
	 ANL   A,R5               ; aktiv ist
	 JZ    TADA               ; Sprung, falls Taste aktiv
	 SJMP  WARTE              ; Modus 0+1 : Taste wieder inaktiv

TADA:
	 SJMP  KEINE_TASTE1       ; Modus = 1 : alte Taste noch aktiv

WARTE:
	 LCALL ENTPRELL           ; Entprellzeit abwarten
	 MOV   A,TASTEN_PORT      ; Pruefen ob Taste noch aktiv ist
	 ANL   A,R5
	 JZ    WARTE              ; Sprung, falls Taste noch prellt

STARTE_ZYKLUS:
    MOV   R4,#0FEH           ; Startwert fuer Ausgabemaske
    MOV   R1,#00H           ; Startwert fuer Tastennummer
    MOV   R2,#P_ANZ         ; Startwert fuer Spaltenzaehler
......

    RET
    
    END

Kind Regards

Juergen B.

Parents
  • +1

    Hi Juergen,

    #include <absacc.h>
// Register Bank 0
#define R1 DBYTE[1]

    Be aware that this most likely does not work as expected, because the compiler is free to re-use R1 at any time. Instead, create a global variable in RAM. You're using C, so you do so (easier):

    data unsigned char MYR1;  // explicitly placed in DATA


    In the ASM file, you refer to it by using EXTRN:

    EXTRN DATA:BYTE(MYR1)
.
.
.
mov MYR1, #012h

    I'm not quite sure what you're really trying to achieve, though. The compiler generates code it assumes to be best for the C you wrote. This is certainly not the same as the hand-written code by you, and you can't tell the compiler to do so. I tend to say: If you don't want to use C then, well, don't use it. Otherwise, write C and stop using assembly language for something as simple as debouncing keys. Use assembly language only directly where you have to or where the code generated really stinks.

Reply
  • +1

    Hi Juergen,

    #include <absacc.h>
// Register Bank 0
#define R1 DBYTE[1]

    Be aware that this most likely does not work as expected, because the compiler is free to re-use R1 at any time. Instead, create a global variable in RAM. You're using C, so you do so (easier):

    data unsigned char MYR1;  // explicitly placed in DATA


    In the ASM file, you refer to it by using EXTRN:

    EXTRN DATA:BYTE(MYR1)
.
.
.
mov MYR1, #012h

    I'm not quite sure what you're really trying to achieve, though. The compiler generates code it assumes to be best for the C you wrote. This is certainly not the same as the hand-written code by you, and you can't tell the compiler to do so. I tend to say: If you don't want to use C then, well, don't use it. Otherwise, write C and stop using assembly language for something as simple as debouncing keys. Use assembly language only directly where you have to or where the code generated really stinks.

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