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I need to replicate the functionality of an expansion board for the Sharp X1 (also Zilog Z80 based). Unfortunately, I don't have too much info to go on about the board or its circuitry - but I know a few things. Basically, it's a line driver board to take the CPU signals and drive them through a long cable into an expansion box.
The lines which are inputs to the box (CPU -> Expansion) are easy enough to work out - they're buffered with SN74LS541 line drivers. Where I'm having difficulty, is understanding the inputs (Expansion -> CPU - NMI, EXWAIT, EXINT, EXIO, IEI) and the data bus.
The data lines (D0-D7) don't actually seem to be buffered at all! But I want them to be.
The others seem to be running through a SN74LS367 bus driver. But I can't work out how the card knows when to enable the *G pin on the 367 and when to tri-state. Or can these chips be configured to tri-state when not at logic 0?
Any pointers in the right direction would be much appreciated. I've not actually had to work with line driving circuitry before.
Many thanks.