Denny Esterline <piclist@mit.edu> wrote:

> I need a simple logic function, a two input AND feeding a two
> input OR feeding another two input AND [see picture]. Since I don't
> need any other logic in the project I hate waste the space and use
> two chips, is anyone else's Boolean algebra less rusty that mine?
> Is there a one part implementation (other than a PAL or CPLD)? 

Danny:

A PIC could do it if you don't mind a six-microsecond propagation 
delay...   

    ; Written for the 12C508A.
    ; 
    ; GP0 = GND
    ; GP1 = A input
    ; GP2 = B input
    ; GP3 = C input
    ; GP4 = D input
    ; GP5 = OUTPUT
    ;
    ; OUTPUT = ((A and B) or C) and D

    LOOP:

        MOVF    GPIO,W
        ADDWF   PCL

        BCF     OUTPUT    ;0000 = 0
        GOTO    LOOP     
        BCF     OUTPUT    ;0001 = 0
        GOTO    LOOP
        BCF     OUTPUT    ;0010 = 0
        GOTO    LOOP
        BSF     OUTPUT    ;0011 = 1
        GOTO    LOOP

        BCF     OUTPUT    ;0100 = 0
        GOTO    LOOP
        BCF     OUTPUT    ;0101 = 0
        GOTO    LOOP
        BCF     OUTPUT    ;0110 = 0
        GOTO    LOOP
        BSF     OUTPUT    ;0111 = 1
        GOTO    LOOP

        BCF     OUTPUT    ;1000 = 0
        GOTO    LOOP
        BCF     OUTPUT    ;1001 = 0
        GOTO    LOOP
        BCF     OUTPUT    ;1010 = 0
        GOTO    LOOP
        BSF     OUTPUT    ;1011 = 1
        GOTO    LOOP

        BCF     OUTPUT    ;1100 = 0
        GOTO    LOOP
        BSF     OUTPUT    ;1101 = 1
        GOTO    LOOP
        BCF     OUTPUT    ;1110 = 0
        GOTO    LOOP
        BSF     OUTPUT    ;1111 = 1
        GOTO    LOOP

        ; A second copy, since we don't know what GP5 will be
        ; when we execute the MOVF GPIO,W...

        BCF     OUTPUT    ;0000 = 0
        GOTO    LOOP     
        BCF     OUTPUT    ;0001 = 0
        GOTO    LOOP
        BCF     OUTPUT    ;0010 = 0
        GOTO    LOOP
        BSF     OUTPUT    ;0011 = 1
        GOTO    LOOP

        BCF     OUTPUT    ;0100 = 0
        GOTO    LOOP
        BCF     OUTPUT    ;0101 = 0
        GOTO    LOOP
        BCF     OUTPUT    ;0110 = 0
        GOTO    LOOP
        BSF     OUTPUT    ;0111 = 1
        GOTO    LOOP

        BCF     OUTPUT    ;1000 = 0
        GOTO    LOOP
        BCF     OUTPUT    ;1001 = 0
        GOTO    LOOP
        BCF     OUTPUT    ;1010 = 0
        GOTO    LOOP
        BSF     OUTPUT    ;1011 = 1
        GOTO    LOOP

        BCF     OUTPUT    ;1100 = 0
        GOTO    LOOP
        BSF     OUTPUT    ;1101 = 1
        GOTO    LOOP
        BCF     OUTPUT    ;1110 = 0
        GOTO    LOOP
        BSF     OUTPUT    ;1111 = 1
        GOTO    LOOP

-Andy  

=== Andrew Warren -- aiw@cypress.com
=== Principal Design Engineer
=== Cypress Semiconductor Corporation
=== 
=== Opinions expressed above do not
=== necessarily represent those of
=== Cypress Semiconductor Corporation

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