Hallo allemaal, Some years ago I saw a photograph of some guys with a board as big as a table with the comment that they succeeded in copying a Z80 only using normal TTL-ICs. That triggered me to do some research my self. But until now I am stuck with one problem: the instruction decoder. My idea about it is a ROM-like construction with the following inputs: - 8 bits instruction code or - 4 (or more) bits special inputs like Reset, IRQ, NMI, SO (future: Abort) - 1 bit instruction/special - Clock-signal - 3 bits countsignal derived from the clock Total of 13 inputs. You could think of a 2764-EPROM but they have one disadvantage: SLOOOOOOOOOW. Another idea is to use Cache-RAMs, I have some of 15ns. They could be used during the test phase but on the end we need a permanent solution. The last thing I am thinking of is to calculate all the equations and build the decoder completely out of gates and decoders. So if anyone has an idea, please let me know. BTW, there is one restriction: for the moment only normal available parts are allowed. So no GALs or PALs for the moment. Groetjes, Ruud - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail email@example.com.
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