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Chuck(G)

  1. Cloning a PAL/HAL (Part 6)

    Part 5 of this series can be found here.

    In the previous post, we discussed using Minilog to derive our GAL equations from PAL raw data.

    We fed Minilog the following data:

    Code:
    table PAL10L8
      INPUT I9 I8 I7 I6 I5 I4 I3 I2 I1 I0 
      OUTPUT O7 O6 O5 O4 O3 O2 O1 O0 
      0000000000 00001011
      0000000001 00001011
      0000000010 00000010
      0000000011 00000010
      0000000100 00000011
      0000000101 00000011
    ...

    Updated June 12th, 2019 at 10:47 PM by Chuck(G)

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  2. Cloning a PAL/HAL (Part 5)

    Part 4 of this series can be found here.

    Rather than pulling hair and drinking lots of coffee trying to manually figure out how PAL inputs are related to PAL outputs, we can investigate some reduction methods.

    If you took computer engineering in school, you probably remember the Quine-McCluskey algorithm. There's plenty of material on the web about it, but it's not particularly efficient, particularly as the number of terms increases. There is also Petrick's Method, ...

    Updated June 12th, 2019 at 10:52 PM by Chuck(G)

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  3. Cloning a PAL/HAL (Part 4)

    You can find Part 3 of this series here.

    Recap thus far: We have a PAL10L8 that we need to duplicate. We've constructed a simple circuit, that driven by a PC parallel port and a bit of software will iterate through all 1,024 input possibilities and record the output.

    We need to get a series of logic equations, one for each output pin that will produce the same results from the input pins as our original PAL.

    We can do this the easy way or the hard way. ...

    Updated June 12th, 2019 at 10:55 PM by Chuck(G)

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  4. Cloning a PAL/HAL (Part 3)

    Part 2 of this series can be found Here

    With the hardware to read the PAL "brute force", all we need is a program to do it.

    Code:
    //	Read a 10L8 PAL and come up with a truth table.
    //
    //		Uses the little board with the 393s
    //
    
    #include <stdlib.h>
    #include <stdio.h>
    #include <dos.h>
    
    #define PRINTER 0x378			// printer base port
    #define PAL_DATA 0x80			// bit representing the
    ...

    Updated June 12th, 2019 at 10:57 PM by Chuck(G)

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  5. Cloning a PAL/HAL (Part 2)

    Part 1 of this blog post can be found here.

    So, basically, the problem boils down to the problem of having a black box with 10 inputs and 8 outputs and having to figure out what's inside. We do know that it's simple combinatorial logic and there's no memory inside. Furthermore, none of the outputs are fed back internally to the inputs, all of which greatly simplifies our task.

    All we have to do is present every possible combination of the 10 inputs (all 1,024 of them) ...

    Updated June 12th, 2019 at 11:08 PM by Chuck(G)

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