On 2012-11-24, at 15:46, Gerrit Heitsch wrote: >>> trying with swapped parts: >>> http://dl.dropbox.com/u/58002657/cbm/c64/epromel_memmap0.png >> >> With limited success as well. >> >> http://dl.dropbox.com/u/58002657/cbm/c64/rom_adapter_narrow1.png >> >> A12 is handled the old way, A 14 is simple: goes LO whenever _CHAROM or _BASIC (A14B) goes low - one '08 gate. But A13 doesn't work. It goes LO whenever _BASIC (A14B) goes LO. So far so good but then it has to be switched via jumper when and /only/ when KERNAL (A14) is HI.. > > A14 on the ROM doesn't work that way. With the gate like this, it means that BASIC and CHAR would have to be in the lower part of the EPROM. The other circuit assumes the KERNAL there. Yes, but I tried to somehow get along without inverting the signals by changing the content map as per the first link above. However even with this I couldn't come up with anything working as I got stuck at the KERNAL switch. > I really see no other way than adding 2 inverters, either discrete or in the form of a 74LS04. > > Also, there is another problem. Your KERNAL-Switch uses the _KERNAL signal which we don't have. I am not particularly precious about what I use for this. I can agree to use anything that works ;-) > We really have to regenerate _KERNAL from !(!A14 & !CS-ROM) which is With the content map as the last one I sort of already had the KERNAL (Active-HI as opposed to _KERNAL): A14 on the EPROM. It didn't help much in such config though. > |\ > A14 ----------| \ |\ > |\ | )----| )O-- _KERNAL > _K/B ------| )O----| / |/ > |/ |/ > > Once we have that, the old circuit and ROM layout can be used again. Since you use a 74LS08, we have enough AND gates, the only thing missing is 2 Inverters: > > +5V > | > | | 4.7K? > | | > | > *----------------- out > | > In ___ |/ > ----|___|----| > |\ > v > | > | > --- > GND Wow! Thanks for the ASCII schematics! I noticed before that you were handy with those! :-) Yes, once we add inverters, things fall back into place and the challenge is over. > If you use a BS170 (cheap FET), you should be able to get by without the input resistor. > > Still not pretty, but the simplest way to fix things IMHO. Another reason for disliking the narrow boards ;-) I shall think what to add there. TRs seem to yield smaller footprint I guess. Thank you Gerrit. -- SD! Message was sent through the cbm-hackers mailing listReceived on 2012-11-24 17:00:06
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