It’s alive! Z-80 Computer hardware now complete.

I have just finished assembling the memory board of my Z-80 homebrew project. All components individually tested, I placed the test program on the ROM, inserted the Z-80 and it worked first time!

It's Alive: Z-80 Homebrew
It’s Alive: Z-80 Homebrew

There is still a little more to do on modifying the I/O board to run the monitor program (which also needs writing) as the board was designed to test the various different circuits. However, the computer successfully executes the following test routine:

;COMPUTER TEST ROUTINE
;
;OUTPUTS ON PORT 0 ANY INPUT ON PORT 0 WHILST CALLING AN EMPTY SUBROUTINE
;
;

LD SP,9000H

L1: IN A,(00H)
CALL TEST
OUT (00H),A
JP L1
TEST RET

This outputs on port 0 any input on port 0 whilst using the stack pointer to save the value of the program counter in the RAM for the execution of an empty subroutine. Thus the I/O, ROM and RAM are all tested. Monitor listing to come soon no doubt.

Z-80 Update

Z-80
Z-80 home brew board
Progress on Memory Board
Progress on Memory Board

Unfortunately, it has been a long time since I could work on my  Z-80 homebrew; it has been in storage for many months. However, my setup is active once more and I have built the processor board. It consists of a power supply, clock, reset logic and buffers for the data, address and control busses. Unlike the I/O board, whose schematic is only in my head, I have used KiCad to design the circuitry and I will upload that separately.

On a separate board lives the I/O decoding and memory, on which I’ve made a start (see picture above). It’s all designed for easy testing and expansion, hence all the chips are socketed. I’ll update soon with the schematics and pictures of the finished article!