On 2012-09-16, at 15:04, Gerrit Heitsch wrote: > After thinking about it for a bit... You can also use a 74LS00 (or 74HCT00) which is fully used up in the process and has 2 pins less: > > How to set up: > > Input1 is A12, it gets fed into one input of one NAND. > > Input2 is your switch. It gets fed into one input of another NAND. Remember the pullup here. > > The select signal (_Char-ROM) is directly fed into the other input of the NAND with A12. It is also inverted by using one NAND (second input tied HIGH) and then fed into the second input of the NAND that takes your switch input. > > The outputs of the 2 NANDs are then fed into the last available NAND and its output is A12 for the EPROM. I did it eventually (and lost last night completely in order for "Inbetriebnahme".. :-) and it works... sort of.. The sort of part is that while the machine boots to BSOL most of the times (and when it does I have both charsets too), sometimes it doesn't. And what's worse whenever I plug in my IDE64 it never boots to BSOL but sometimes shows an interesting picture: http://dl.dropbox.com/u/58002657/cbm/c64/2012-10-07%2012.29.07.jpg (note the vertical bars in the border - probably some kind of Soci's signature? - and the charset too) and sometimes just ends with a black screen.. any ideas? I used 200ns EPROM but checked also faster ones with the same or worse results. My 150ns for example never booted to BSOL nor showed the IDE64 mysterious screen. 120ns behaves similar to 200. While it doesn't make much sense, I still tried uncoupling the _CS from _OE but as expected there was no difference in behaviour. Something is really strangely off / on the verge of specs here. Any help ideas? -- SD! Message was sent through the cbm-hackers mailing listReceived on 2012-10-07 11:00:05
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