Electrical – Z80 computer design peer-review


this is a re-post as I was unable to get any help on other forums. I have designed and built a simple Z80 computer system with 32K RAM, Z80B at 4mhz, 32K ROM, and a UART. The only problem with it is that the system doesn't seem to work. So, I am asking to have somebody peer-review my code and schematics.

    org 0x0000
    ld a, 0x80
    out (0x03), a
    ld a, 12
    out(0x00), a
    ld a, 00
    out(0x01), a
    ld a, 0x03
    in a, (0x05)
    bit 5, a
    jp z, uart_out
    ld a, 0x41
    out (0x00), a
    jp uart_out

Z80 System Processor
Z80 System IO
Z80 System Memory

Best Answer

Are you absolutely sure that this is the correct way to connect a bus:

enter image description here

Every schematic package that I have ever worked with had special provisions for depicting BUS connections that were different from how single wire nets are connected. As shown in your schematic it would appear that you have shorted all the data bus pins together and all the address bus pins together. If this is the case it is no wonder that it does not work.