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Approaching a final design of the Internal Bus

07/07/2009

Looking for standards I got to the VME Bus P1 which utilizes the same 96-PINs connector I chosen. This bus is designed for computers and it designates many power and control lines that I don't need for my Internal Bus, but I decided to adopt the pin out discarding those signals that I don't use but retaining those that I do; these are: 16 Data pins, 16 Address pins, SYS CLK, 8 GND pins and 3 +5V pins. Discounting the rest out, I have 53 extra pins for anything else.

I started wondering if that would be enough for my control signals, that is if my previous forecast of about 70 were currect. In order to approach the answer, I did a detailed signals count over the CPU block diagram. The final pin-count surprised me: only 46.

Of course, in practice they will be more and there will also point-to-point connections between certain cards. But it still makes sense to consider the 53 extra pins for a possible "control signals bus".