Atari ST - dumping/reading ROM chips - which IC?

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LukaszCJokiel
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Atari ST - dumping/reading ROM chips - which IC?

Postby LukaszCJokiel » Fri Nov 08, 2019 8:13 pm

I've got a pretty dead Atari 1040 STfm, showing just a single white line (other one I got - STE works fine with the 15kHz H capable VGA monitor). I suspect the ROM's to be at fault, and using TL866II I can program the appropriate compatible EEPROM for example - for the the STE in DIP32 package. But here I got DIP28 and no source EEPROMs.

But for this fault Atari 1040STfm I got two: C300689-00A and C300690-00A chips which is identfied as German TOS 1.04 (keyboard is German too).

The questions is - how can I read those IC/chips what's the actual model? Windbon? What did Atari use here? I want to check if the ROMs are actually good - so reading/dumping them, joining and trying to run in Hatari as source ROMs.

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Arne
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Re: Atari ST - dumping/reading ROM chips - which IC?

Postby Arne » Sat Nov 09, 2019 7:45 am

These are Mask-ROMs. They omit the pins needed for programming and replaced them with additional address lines. So you have to build an adapter to read them in an EPROMer. Or put them into another ST and check them. Or you add four 28pin sockets onto the mainboard and put six 27C256 (or compatible Flash/EEPROM) into these sockets.
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frank.lukas
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Re: Atari ST - dumping/reading ROM chips - which IC?

Postby frank.lukas » Sat Nov 09, 2019 7:53 am

.. or you can also use two 27C010 Eproms 32pin and mod them -> https://www.exxoshost.co.uk/atari/last/ ... #tos102104
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LukaszCJokiel
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Re: Atari ST - dumping/reading ROM chips - which IC?

Postby LukaszCJokiel » Sat Nov 09, 2019 10:35 am

Thanks, my goal was only to dump their contents to see if they are at fault. But luckily I found the forggoten STF with same ROM configuration and it seems that this TOS is 100% OK.

Well of I go then - this is 1040STF German, and it doesn't boot - floppy tries to read the disk, but all I got is white screen in LOW-RES mode or single white-line in HIGH mode. The shifter area has some bad looking solder on the back, so resolder is definetly needed there.
Thanks for the idea with Exxos modding the newer chips to older DIP28 sockers.

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Re: Atari ST - dumping/reading ROM chips - which IC?

Postby tzok » Sat Nov 09, 2019 12:50 pm

If you have 6 28 pin ROMs, then you may read them as 27C256 EPROMs. Only 1 Mbit ROMs had different pinout than EPROMs, 256 kbit ROMs are pin compatible with EPROMs (as for reading of course). Reading does not require any vendor specific conditions, so you may choose any IC manufacturer you want.

For 2 ROM machine, you could easily replace them with 27C1000, or with some more hassle with 27C010.27C1001.

For switching from 2 to 6 EPROMs you need to change some jumpers/bridges. Changing from 6 to 2 usually requires adding one IC.

Atari branded ROMs could be either Mask-ROMs or OTP EPROMs actually. Mask-ROMs are very unlikely to fail.

LukaszCJokiel
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Re: Atari ST - dumping/reading ROM chips - which IC?

Postby LukaszCJokiel » Mon Nov 11, 2019 8:20 pm

Thanks, I'm looking at them but they seem to be not compatible with Xgpro database.


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