The Dos and Don'ts of using an EPROM as PLA in a C64.

Disk drives, Monitors, SuperCPU etc.
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eslapion
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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by eslapion »

@banman
Gyro Gearloose is more of an expert than I am with really old circuits. I truly don't know what these are.

Can I encourage you to keep this thread specifically about using memory chips as PLA in the C64 or other Commodore 8 bit computers ?

If you want to discuss antique electronic parts you managed to acquire, please start another thread about this subject. You never know, there may be lots of other people who found interesting stuff too.


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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by banman »

Hi eslapion,

Sure , I absolutely agree.
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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by banman »

Hi Eslapion,

I have mananged to get the Tektronix oscilloscope working and calibrated. Passes all the start up tests ok. Been testing a few points on a working C64.
Appears to display the correct wave forms as compared to a C64 service manual.

Just need to learn how to capture and store randomly occuring events now.

May take a little bit of time....
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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by eslapion »

banman wrote: Thu Sep 26, 2019 5:38 am Hi Eslapion,

I have mananged to get the Tektronix oscilloscope working and calibrated. Passes all the start up tests ok. Been testing a few points on a working C64.
Appears to display the correct wave forms as compared to a C64 service manual.

Just need to learn how to capture and store randomly occuring events now.

May take a little bit of time....
You sure like it the complicated way!

I have my TDS1002 since early 2003, was calibrated in 2002 and I recently tested against a few oscillators for timing reference and a 5V reference source and it's just as good today as it was when I bought it.
Wealth, like happiness, is never attained directly. It comes as a by-product of providing a useful service. -Harland D. Sanders
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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by banman »

Hi eslapion,

You are very right! LOL :-)

I am glad this is a hobbie and not my day job.


It has been an amazing learning curve to me. I have done and learned things I never really thought possible of myself. I am a true Luddite.....


I am really keen on seeing my results compared to yours with this thing I observed with the Chinese knockoff ST 27c512 OTP PROM.

:)
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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by banman »

Hi eslapion,


I have made some initial observations of the substitute EPROM based PLA's with an oscilloscope.



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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by eslapion »

There is something really wrong with the settings on your scope.

The measures indicate 40 to 60mV p-p but when you turn on your C64, the line should jump from 0V to around 4.3V and I see no DC in there and no information about it in your measures.

Remember the scope captures included in the 2nd and 3rd posts at the very beginning of the thread. This is pretty much what you should see on the screen of your scope if it is configured correctly.

Min and max voltages are more important than p-p which you can calculate by simply doing Vmax-Vmin. Vmin should never go lower than about 2.5V.
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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by banman »

Hi eslapion,


Thanks for that ... :oops:


I will go back and check the settings again.....

I will go back over your 2nd and 3rd posts and get my oscilloscope set out like yours..


Should I have the attenuation set to DC instead of AC?

CH1 1.5v divisions on the graticule scale

40ns sweep-time

Is that a trigger on the down slope?

I appreciate your patience with me :D
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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by banman »

Hi eslapion,


Wait a sec!


I think the probe is set to 10X ....

That would throw the readings as well out for sure...


Opps!!!
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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by eslapion »

banman wrote: Tue Oct 08, 2019 9:45 am I think the probe is set to 10X ....
That's the correct setting.

The trigger should be set around 3V for a falling edge and the channel should be set to DC.
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