On 2012-05-14, at 12:56, Gerrit Heitsch wrote: > - Build an adapter to use a 27xxx-EPROM in the socket of a 24pin 2364 ROM. Most of it is 1:1, just a few lines need to be rerouted. Do not connect the _CS line directly. Place it either into the KERNAL or BASIC socket. > > - Connect all 3 _CS signals for the ROMs to the 3 inputs of one of the gates of the 74LS11. The output goes to _CS and _OE of the EPROM. > > - Also connect two of the _CS-Signals to A13 and A14 of the EPROM. > > The 74LS11 is a 3-input AND gate. So when the CPU wants to talk to one of the 3 ROMs, one of the inputs of the AND goes LOW, resulting in the output going LOW and activating the EPROM. Which part of the EPROM gets selected is also done by 2 of the _CS lines. You just need to put the 8 K BASIC and KERNAL and the 4 K char into the right parts of the EPROM. Could you have a look at: https://dl.dropbox.com/u/58002657/rom_replacement.png > The 8 K block where A13 and A14 are both low stays empty. I didn't like this sentence ;-) Especially that second KERNAL (DolphinDOS, Jiffy, ..) is really good thing to have. That's why I put the jumper and used the second gate. I am somewhat unsure about the pullup R302 but generally the idea should do the trick, right? Any comments? TNX in advance. P. S. I am still thinking of dropping in a second charset too. Like the one from C128 and have ASCII/DIN switch. -- SD! Message was sent through the cbm-hackers mailing listReceived on 2012-09-15 00:00:05
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