Showing posts from December, 2014

Register Design: Instruction Register

Well, it's fair to say that I rather underestimated just how much time decorating the new house would take up ... and that's mainly because 'decorating' included re-wiring, re-plumbing, re-plastering, re-carpeting ... all before I got anywhere near choosing a tasteful shade of emulsion for the walls. Needless to say then that spending time on my relay computer has suffered quite a bit. However, things are starting to calm down (now that there's two rooms in the house that are semi-habitable) so I can get back to designing the next bits for the computer.

The next card up for design is the (mercifully straightforward) 8-bit instruction register. I say straightforward as this card shares much of its design with the B/C register card already constructed. The instruction register is permanently connected to the instruction bus just as the B/C registers are permanently connected to the ALU. However where the B/C registers are general purpose, and so can be set from and …