HP9816 PAL16L8

[Paul Berger]

On 2019-06-11 1:19 a.m., Chuck Guzis via cctalk wrote:
> On 6/10/19 8:44 PM, Tony Duell via cctalk wrote:
>
>> You can detect sequential logic in the PAL by :
>>
>> For each combination of inputs :
>>     Read the outputs
>>       Toggle an input (change from 0 to 1 and back again or vice versa)
>>       Compare the outputs to what they were before -- if they have
>> changed then there's a sequential function on that input
>>       Check the next input
>>    Check the next combination of inputs
> For purely combinatorial PLDs, see my blog entry on the subject over at
> vcfed.org; I did the work to clone a few PALs some years ago and
> documented the process.
>
> FWIW, the setup to do this was a few TTL ICs connected to the parallel
> port of a PC.   Nowadays, I'd probably do the same with an inexpensive
> MCU--the programmable nature of MCU pins lends a certain amount of
> flexibility to the process.
>
> Basically, you separate the inputs from the outputs and then run all
> combinations of the inputs, observing the outputs.   If the tristate
> feature is used on outputs, there's a way to discover the difference
> between a tristated pin and a genuine input.
>
> There are a number of tools to perform reduction on the results, such as
> Logic Friday.   After that, you're left with a bunch of logic equations
> that can be fed into a PAL/GAL assembler and programmed.
>
> --Chuck

Old computer work too, I used a GPIO in a HP 9000-332.  Years ago I also 
created general purpose I/O ports for a PC using 6821 chips since they 
are way more flexible that the Intel  8255, but the HP 9000 coupled with 
RMB makes for a great environment to bang out quick programs to do 
things like this.

Paul.