Register File building start

A project log for ECM-16/TTL homebrew computer

16 bit Computer made from ttl logic chips

PavelPavel 04/08/2021 at 17:541 Comment

This entry is just an announcement of start of building the Register File component (previously described here). It should serve as the statement of commitment.

The Register File will have eight 16-bit registers, and their selection logic.

Here is how I envision its boards arrangement: there would be just 3 big boards ( two 8-to-1 multiplexer boards: selector for Src1 and selector for Src2, and one "RF backplane" board, which will have a handful of chips on it and 8 slots for small register boards), and 8 small boards each having two 74HC273 chips and LEDs indicating content and selection status. The individual small register boards are to be connected to "RF backplane" through pin header connectors.

I am not sure if I need single interface board similar to one I've done for ALU

Overview schematic of Register File to be built:


zpekic wrote 04/11/2021 at 03:28 point

Hi! Cool project, 16-bit CPUs can be powerful! Did you consider using the venerable 7489 chips? With the same amount (8) you could have a dual output 16*16 register file. If your design uses 8 regs, you can have A3 select fast one "bank" or the other (similar to Z80 "EXX"). 8 are needed for the old trick of be able to simultaneously read 2 registers: Read: each block gets own read address (DOUT is separated), Write: both block gets same write address and DIN is the same. 

The other idea is to combine ALU + reg into single board, and then 4 of those make the complete CPU. 74181 + 2 7489 + some MUXs are equivalent to home-brew "4-bit slice" - such slice can then be reused for other projects too.

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