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A project log for Z80 Computer

An attempt to build a Z80 computer capable of running CP/M

techavtechav 12/19/2015 at 04:010 Comments

After the HAD article [Brandon Dunson] wrote about Tanner Electronics, and the subsequent realization that I'm only 30 miles away, I had to go check it out. Two hours and $35 later, this project has new life.

I picked up a 1.8432 MHz crystal and an oscillator of the same speed. It should be a good clock rate for the UART, and I think it would make a good rate for the main system clock as well. I also grabbed a couple 62-pin card edge sockets (ISA, anyone?) so I could experiment with mounting various sections of the computer on boards (à la [Quinn Dunki]), and I got a CompactFlash socket for booting CP/M (à la [Grant Searle] (whose web host blocked on all AT&T services)). For the sake of my future MC68000 project I got a couple 30-pin SIMM sockets (though if I can figure out the refresh, I might pull one into this project).

Most exciting of all though, Tanner's actually had the Z80 DMA. The DMA is the the hardest to find of the Z80 set. Mouser still carries the SIO, SCC, PIO, CTC, etc, but not the DMA. And since they had them, I did picked up a PIO and CTC. This means now I have a complete peripheral set for the Z80, and I'll be going back to almost to square one.

I'm thinking this time I'll do without the buffers. They worked, but I think they may have been the source of some of my problems when I tried running slightly more complex code. I do wish I had an oscilloscope to properly investigate it though. I'll probably keep my ROM/RAM setup the same, with a 32kB ROM swapping with the lower 32kB of RAM. I'll probably also stick with the '154 for IO address decoding, and the flags register for the ROM/RAM swap.

Now, planning is all well and good, but the project already got put on hold for one move, and another is coming up soon. So, I don't know when I'll actually get to sit and work on this again, but at least it's back on the front of my mind. As anxious as I am to sit down and draw it out, I should probably finish my weather display first, before it ends up permanently stuck in the limbo of the projects bin.