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Running a Program on WDC-1

A project log for WDC-1 a "Working Digital Computer"

Make a computer based on the book "How to Build a Working Digital Computer" by Edward Alcosser, James P. Phillips, and Allen M. Wolk

Michael GardiMichael Gardi 01/15/2020 at 22:170 Comments

With everything together I wanted to do something interesting on my Working Digital Computer Version 1 so I wrote the following program to calculate the first few numbers in the Fibonacci sequence (which we know starts with 0, 1 and that each subsequent element is the sum of the previous two numbers in the sequence (so 0, 1, 1, 2, 3, 5, 8, 13...)).

        ; Calculate the first few Fibonacci numbers.
        ; Assumes that the first two numbers 0 and 1 are in the
        ;  INPUT Encoder A and Encoder B addresses.
        ;
1000 1000    RIN    A        ; Read the first seed
0110 0000    TRA             ; Transfer A to X
1000 0100    RIN    B        ; Read the second seed
0001 1100    STO    C1       ; Save the last number
0100 1101    ADD    4        ; A + X  Result in A
1110 0011    RUT    1s       ; Result < 10 show in OUTPUT
0001 0010    STO    C2       ; Remember result
1000 1100    RIN    C1       ; Get last number
0110 0000    TRA             ; Transfer A to X            
1000 0010    RIN    C2       ; Get current result back
1010 0001    SHL    1        ; Is the current result >= 8?
1001 0001    COJ    1        ; Result >= 8
1000 0010    RIN    C2       ; Get current result back
0001 1100    STO    C1       ; New last number
0101 1101    JMP    4        ; Go back to add
1101 0001    ENJ    1        ; Jump to location
1000 0010    RIN    C2       ; Get current result back
0100 0000    ADD             ; A + X  Result in A
1110 1111    RUT    BCD      ; Convert binary to BCD put result in OUTPUT
0000 0111    NOP    ANS      ; Final result

The hardest part was keeping the program length down to 20 instructions, the current limit for my "low density" drum memory.  I'll have to get going on the "high density" drum if I want to do more. I've "run" the program a few times and it seems to operate as expected.  I guess my current thinking is to make a video of WDC-1 in action. 

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