Klyde

Thank you ClausB, I have followed your advice and redirected /S7 on pin 18 and A12 on pin 20 and... If there is something I can do for you guys, just let me know... Cheers! Happy Klyde

As simple as that! Brilliant! I'll try that and let you know. Many thanks for helping me out! Cheers, Klyde

Thank you ClausB, this is clear! I didn't take A12 into account. I definitely need to learn how CPU address spaces and memory address decoding work! If you have any ressource or books to point me, don't hesitate, I only have a basic understanding of all that. Correct me if I am wrong, but I should end up with something like this? And I keep /OE grounded (always enabled), right?

It appears that I may have difficulties to find a 2332 eprom, they are quite rare. I am going to stick to the 23xx adapter link you provided.

Thank you BillC, I got it! The CO15199 is not a 2532 but a 2332! I am going to try to have a 2332 eprom programmed. Cheers! Klyde

Thank you Paul! I forgot to mention I did an unboxing video of this A400:

Hello guys, I am an Atari fan and collector of 8-bit computers and consoles. I live in France, and some of you already know me as I am a member of The Atari Owner's Club https://atari-owner.com/club/ I own several 600/800XL and 65/130XE machines, Atari STE and STF, TI 99, MSX, Oric, Amstrad... well, you name it, plus obscure French computers you probably never heard of... I also sell an Atari 2600 SECAM RGB video mod, among other things, on my website: http://klydes-korner.site/ I try to refurbish and maintain them all, and I have for that all the equipment needed: soldering station with hot air, bench power supply, multi-meter, oscilloscope, logic probe (but no logic analyser), RAM tester, EPROM programmer, etc. though my knowledge in electronics is somewhat limited when it comes to read schematics. Today I need the help of some experts in electronics, with an Atari 400 PAL machine I bought as spares or repair 2 month ago. The CPU, POKEY and one of the OS ROM chip (CO15199) were missing. I have replaced the missing CPU and POKEY with known good spares I had. By testing the other chips, I found out the ANTIC was bad, as well as one RAM chip. I replaced them too. All the other chips, including 74xx logic chips were tested ok. The power supply is ok, and the various voltages +5V, -5V, +12V, are present across the board. I also have installed a UAV (thank you TBA, it works like a charm). The Atari 400 main board About the missing CO15199 OS ROM, I couldn't find a spare one (not a surprise) except at Best-Electronics, but I can't (and dont want) to buy from them, as they won't let me buy only one $8.00 chip, plus it would cost me a lot more in shipping fees. So I wanted to try to "emulate" the CO15199. I read somewhere (maybe here?) it was a kind of 2532 ROM chip, so I programmed a 27C32 EPROM with the correct dump image (rev. A PAL ROM file), and I built an adapter with a strip board, since the 27C32 is not just a drop-in chip. The adapter board I made - The 74LS04 was here for signal testing purposes But I am facing an "oddity" with the real CO15199 I can't sort out: it has two CS pins (a CS# and a CS pin), whereas the 27C32 only has one CS# pin. I know what a CS# signal is, and what "active LOW" and "active HIGH" signal means, but I can't figure out how both CS# and CS do work together (if they do?). According to the schematics: Atari 400/800 Field Service Manual p.43 CO15199 ROM "E" (A104): CS# is connected to pin 9 of a 74LS42 (which is an output pin). CS is connected to pin 6 of a 74LS138 (which is an input pin). I am ok with the CS# pin but, what is the purpose of the CS pin? - My first thought: CS# and CS are tied together internally with an inverter: the 74LS42 "drives" the CO15199 with the CS# signal, the CO15199 invert the signal internally to "drive" the 74LS138. But I tried to do some testing of this theory on a breadboard and on the Atari 400 itself (hence the 74LS04 on my adapter board), but had no good results. - Second thought (most likely?): CS# and CS are both needed, CS# has to be LOW and CS has to be HIGH at the same time to select the ROM chip. - Third thought (unlikely?) : CS# and CS are not related, but the signals can be emulated somehow. - Fourth thought (unlikely?): CS# and CS are not related, should be considered as two independent signals and can't be emulated. The only result I have so far is the Red Screen of Death. Is it possible to emulate the CO15199 with a 27C32 or other EPROM? Or am I loosing my time trying? Did one of you do it already? What do you think? If it is not possible to replace it with a 27C32, do some of you plan to place a joint order to Best-Electronics in a near future and would be ok to order a CO15199 on my behalf and send it to France? Thank you for reading me.

Hi! Nice you can help us, very kind of you. I'll provide the firmware, a Winculp code is ok for you? Klyde