Completed and Rebuilt XY Register

A project log for 8 Bit Breadboard CPU

A home-brew 8 bit Microprocessor built on a breadboard 64K Address Space, IRQ, and DMA 16 Bit Stack Pointer, 4 8 bit Registers or 2 16 bit

2-Zons2-Zons 01/12/2019 at 04:320 Comments
Complete XY Register

I started over and completely rebuilt the XY register.  I was having trouble with the bus drivers.  I switched to 74HC245's from 74ACT241N's.  The 241's were  actually dual 4 bit buffers each with their own enable line (one active hi and one active lo).  The enable lines couldn't be tied together and each 4 bits was output on opposite sides of the chip which made wiring really messy.  I also got new wire delivered which is the same guage (22AWG) but has a thinner insulator and is much nicer to work with.  I've tested out all the functions and they all work:  X inc and dec; Y inc and dec; XY inc and dec; load XY from address bus; load X or Y from data bus; push X or Y to databus; push XY to address bus; and reset.  Only thing left is some control signal logic which I am missing some OR gates to complete.  I neglected to order them earlier.  I think I'll build the ALU next.