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Write R7 register directly from C

Vu Lam Dien

I use KeilC uVision4 for 89C51 MCU.
By "Inline ASM", i can easily direct write value to R7 register, like this :

    #pragma ASM
        MOV R7, #10
    #pragma ENDASM


But now, there are some reason that i have to write to R7 register direct from C (not from inline ASM), eg:

    R7 = 10;


Of course, the C compiler does not understand R7 as MCU Register (not Inline ASM).

-> Is there anyway to solve this problem. Please help me if anyone know, thanks a lot !

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    Well, I intend to write an Accurate "ASM Delay Routine" by "Inline ASM".

    Let take the simplest delay code:

        #pragma ASM
    MOV R1, #vR1
    // Calculate Time spent From Here
    DJNZ R1, $ //2 Machine cycle (MCs)
    #pragma ENDASM


    With 8051MCU, it spent : t1 = vR1 x 2 machine cycles (MCs)

    Now, with 2 registers used:

        #pragma ASM
    MOV R1, #vR1
    MOV R2, #vR2
    // Calculate Time spent From Here
    DJNZ R1, $
    DJNZ R2, $-2
    #pragma ENDASM


    time spent : t2 = (t1 + 257vR2 - 256) x 2 MCs

    Finally, with 3 registers used:

        #pragma ASM
    MOV R1, #vR1
    MOV R2, #vR2
    MOV R3, #vR3
    DJNZ R1, $
    DJNZ R2, $-2
    DJNZ R3, $-4
    #pragma ENDASM


    time spent : t3 = (t2 + 65793vR3 - 65792) x 2 MCs

    Generraly, with n Register used, we can delay :

    tn = (tn-1 + (Cn-1 + 1)vRn - Cn-1) x 2 MCs
    where :

    Cn = 256^n + 256^(n-1) + ... + 256 + 0

    Now i write a delay 3000MCs routine :

    //8051 MCU
#define Interval 3000 // Change here to change delay in MCs)

#define C0 0                 // Constant in formula above
#define C1 256               // Constant
#define C2 65792             // Constant

#define t3 Interval/2        // DJNZ take 2 MCs, so divide by 2 for easier calculation
#define vR3 ((t3+C2-2)/(C2+1))   // Calculate R3 value

#define t2  (t3+C2-(C2+1)*vR3)
#define vR2 ((t2+C1-1)/(C1+1))   // Calculate R2 value

#define t1  (t2+C1-(C2+1)*vR2)
#define vR1 ((t1+C0-0)/(C0+1))   // Calculate R1 value

void Delay() {
    #pragma ASM
    MOV R1, #vR1
    MOV R2, #vR2
    MOV R3, #vR3
    DJNZ R1, $
    DJNZ R2, $-2
    DJNZ R3, $-4
    #pragma ENDASM
}


    Use in main routine :

    void main() {
    Delay(); // Delay 3000 Machine Cycles
}

    => For easier use, i should write a DelayMCs() Macro, eg :

        #define DelayMCs(Interval) //Code Here???


    Then, use this Macro like this :

    void main() {
    DelayMCs(7000);
}


    => That's my idea. But i don't know how to write this Macro. Can anyone help me build "Code Here" above. Thanks !

Reply
  • 0

    Well, I intend to write an Accurate "ASM Delay Routine" by "Inline ASM".

    Let take the simplest delay code:

        #pragma ASM
    MOV R1, #vR1
    // Calculate Time spent From Here
    DJNZ R1, $ //2 Machine cycle (MCs)
    #pragma ENDASM


    With 8051MCU, it spent : t1 = vR1 x 2 machine cycles (MCs)

    Now, with 2 registers used:

        #pragma ASM
    MOV R1, #vR1
    MOV R2, #vR2
    // Calculate Time spent From Here
    DJNZ R1, $
    DJNZ R2, $-2
    #pragma ENDASM


    time spent : t2 = (t1 + 257vR2 - 256) x 2 MCs

    Finally, with 3 registers used:

        #pragma ASM
    MOV R1, #vR1
    MOV R2, #vR2
    MOV R3, #vR3
    DJNZ R1, $
    DJNZ R2, $-2
    DJNZ R3, $-4
    #pragma ENDASM


    time spent : t3 = (t2 + 65793vR3 - 65792) x 2 MCs

    Generraly, with n Register used, we can delay :

    tn = (tn-1 + (Cn-1 + 1)vRn - Cn-1) x 2 MCs
    where :

    Cn = 256^n + 256^(n-1) + ... + 256 + 0

    Now i write a delay 3000MCs routine :

    //8051 MCU
#define Interval 3000 // Change here to change delay in MCs)

#define C0 0                 // Constant in formula above
#define C1 256               // Constant
#define C2 65792             // Constant

#define t3 Interval/2        // DJNZ take 2 MCs, so divide by 2 for easier calculation
#define vR3 ((t3+C2-2)/(C2+1))   // Calculate R3 value

#define t2  (t3+C2-(C2+1)*vR3)
#define vR2 ((t2+C1-1)/(C1+1))   // Calculate R2 value

#define t1  (t2+C1-(C2+1)*vR2)
#define vR1 ((t1+C0-0)/(C0+1))   // Calculate R1 value

void Delay() {
    #pragma ASM
    MOV R1, #vR1
    MOV R2, #vR2
    MOV R3, #vR3
    DJNZ R1, $
    DJNZ R2, $-2
    DJNZ R3, $-4
    #pragma ENDASM
}


    Use in main routine :

    void main() {
    Delay(); // Delay 3000 Machine Cycles
}

    => For easier use, i should write a DelayMCs() Macro, eg :

        #define DelayMCs(Interval) //Code Here???


    Then, use this Macro like this :

    void main() {
    DelayMCs(7000);
}


    => That's my idea. But i don't know how to write this Macro. Can anyone help me build "Code Here" above. Thanks !

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