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Category: Z-80

Start of a new computer, just a 7805 regulator.

Z-80 Homebrew MkII

I need to come up with a good name for this project… Anyhow, after my previous prototype I have decided to built a Z-80 project anew. Basically, the issue with the previous was lack of UART (I built one, had it working, then accidentally blew it up), the different boards and the masses of wires making the computer unstable and legs of my flash ROM getting bent from too much insertion and removal. Therefore, this one will all be on the same board, have custom sockets for expansion and a built in UART. I will also add a ZIF socket…

It's Alive: Z-80 Homebrew

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! 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)…

Z-80 Update

Unfortunately, it has been a long time since I could work on my ┬áZ-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…

Z-80 I/O

Z-80 Homebrew: I/O board!

The next step on my Z-80 journey is building the I/O. I decided to do this before building the processor circuit itself as it doubles up as a handy test device. There are three output ports that use TIL311 displays; I got these cheap off eBay from Hong Kong. They take a four-bit input and display it as a hexadecimal value. Therefore, in pairs, they can display binary data from the data bus as a hexadecimal number 00h – FFh. They aren’t all connected to the data bus; I’ve kept them separate, so if necessary I can connect them to…