27C400/27C800 EPROM emulator

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PaulJ
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Re: 27C400/27C800 EPROM emulator

Post by PaulJ » Wed Feb 05, 2020 4:00 am

Well, built a prototype board to use the rom emulator on a mega4 but have achieved no joy. Programmed byte reversed and not reversed both work the same. Video garbage is the best I have achieved. Diagrom just gives a white screen. Assuming Lighting ST provides a cs for $FC000, $E00000, and 0 through 7 since it takes cs from the mega4 rom pin 20 u9 or u10.
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cmorley
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Re: 27C400/27C800 EPROM emulator

Post by cmorley » Wed Feb 05, 2020 7:41 am

I can't speak for the /CS & /OE on that system. I assume you tied /byte to Vcc. Any of A18, A19 and R which are not connected should be set to pull up in the module's software. The STM32 has open-drain outputs so without pull ups (internal or external) the voltage will be floating.

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Re: 27C400/27C800 EPROM emulator

Post by PaulJ » Wed Feb 05, 2020 2:57 pm

I have connected /byte to +5. I received the second unit replacement yesterday in great shape... thanks for the additional packing Chris. So I will give that one a try. The current unit works great from the USB side but the no echo on input makes me crazy. Hope you will fix that on newer versions of the software. Also there is a lot of unknowns in the operation so a manual or a README down the line will be appreciated. But as far as the USB operation is concerned it always writes and verifies fine.

Guess I'm going to need to generate my own decode so I can boot off the standard 1.04 rom and examine the code at $e00000. Also I'll purchase a real 27c400 to verify the prototype adaptor. I may try the Atari dogcart with serial. It my get far enough in the code to get that working but I doubt it.

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