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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Re: 27C400/27C800 EPROM emulator

Post by PaulJ » Mon Mar 09, 2020 9:42 pm

@cmorley , just curious.. are you still selling them?

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Re: 27C400/27C800 EPROM emulator

Post by cmorley » Tue Mar 10, 2020 7:41 am

Sure, I have a few left built up and can always build more if people want them.

I am working on a comprehensive test for them. Got a few things on the list for the firmware too. Plus life gets in the way - so still active on this just quietly with nothing useful to report to the forum.

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Re: 27C400/27C800 EPROM emulator

Post by PaulJ » Tue Mar 10, 2020 10:02 pm

@cmorley I would like a couple more in the hardpak. You can leave the pins unsoldered. I can do that here. Let me know the price and I'll pay you via PayPal. Building a prototype adaptor for the H4. Eventually I'll have to make pc boards. :) :)

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Re: 27C400/27C800 EPROM emulator

Post by cmorley » Sun Mar 22, 2020 9:20 pm

Contract work has been keeping me busy but I did a bit of work on the firmware tonight.

I've added a proof of concept ROM switch if no A0 activity. This should mean on Amiga (at least) you don't have to fit the /RST wire for basic ROM switching. If you want to reset the machine from USB then of course you need one.

I use a register in the CPLD to watch for a rising edge of A0 (on the EPROM) - on the assumption if the CPU is executing code from ROM or RAM then 68000 A1 ought to be toggling. I read that register out over the serial link between the STM32 and the CPLD.

I quickly hacked it in to the STM32 firmware and it works it seems. Interestingly Kickstart 3.1.4 seems to stop and think for 20ms at a time (does it do a halt then wait for v-sync?)...

I've got more code to do to add this properly to the C firmware, then I'll release a firmware upgrade.

One macro cell free in the CPLD - what function can I add to get 100% utilisation :roll:

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Re: 27C400/27C800 EPROM emulator

Post by PaulJ » Sun Mar 22, 2020 9:37 pm

@cmorley , it sure would be sweet if when entering programing parameters they didn't need to be entered in the blind. Also I have received the additional two I ordered but haven't tried them as of yet. Thanks for the quick turn around. :)

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Re: 27C400/27C800 EPROM emulator

Post by cmorley » Sun Mar 22, 2020 9:41 pm

PaulJ wrote:
Sun Mar 22, 2020 9:37 pm
@cmorley , it sure would be sweet if when entering programing parameters they didn't need to be entered in the blind.
I'll look at something. I really don't have a lot of code space left ~170 bytes IIRC. You could turn on local echo on your terminal program for now.

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Re: 27C400/27C800 EPROM emulator

Post by rubber_jonnie » Fri Mar 27, 2020 9:07 am

@cmorley I saw you mention a bit further up you may still have some for sale, and I am interested in 1, maybe 2. Could you let me know a price please?
Collector of old Atari things:
800XL + Ultimate 1MB, 2x 1010 cassette, 1050 + Happy mod, 65XE (128k +APE Warp) & XC12, SIO2SD, 2600jr, 7800 and Lynx II
Atari 520ST (1Meg), 1040STF long button floppy, 2x 1040 STFMs + Gotek, 2x 4160STE with 32Mhz booster, ROM switcher, Mega ST1, Mega ST4, not to mention various bare ST boards for testing including a PAK 68/2 :)
Plus the rest..
Amiga stuff, Mac stuff, Sinclair stuff etc...
www.electronicnothingness.co.uk

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