homebrew Z180

[norwestrzh]

Here's my homebrew version of the Z-180 design by Stephen Cousins (SC-131). It's very small -- fits on a 100mm x 100mm PCB. It could be lots smaller, but I added some footprints for alternative EEPROM that I wanted to experiment with. Right now it runs with a PDIP Winbond W27C512 (64k) in a socket set up for a SST 512k EEPROM (selected by the jumper just above the chip). I also want to try PLCC versions of that chip, and a 128k SST chip (empty footprints). "Disk" is on the level-shifting uSD adapter (red PCB). It boots up Wayne Warthen's ROMwbw (very nice software!). I'm using a wall wart to power it, but wondering if it is low power enough to run directly from the USB adapter that provides the console? Something to investigate. Oh, and the console comes up at 115.2k baud, but that's too fast to do XMODEM downloads. I have to turn it down to 38.4k for that!

Roger

 

[Plasmo]

I can not read the oscillator value. Is it 18.432mhz? The Z180 you are using is rated to 33Mhz and good for 36.8Mhz, so you can double the clock, but the rest of memory and logic probably won’t keep up. RomWBW auto detect the serial baud, but that needs a RTC, so without RTC, it defaults to 38400. You can change the serial baud in RomWBW with ‘I’ command before booting to CPM with ‘C’ command

Now I noticed the forum has a home brew computing group. I should put some of my designs there.
Bill

 

[bsd64]

Great design! I own the SC-131 from Cousins and it runs using only power from the usb port (it's listed to use 100mA without the SD card and up to 300mA with SD). It's a really nifty little computer. I feel the Z180 may be underappreciated for these retro-computing designs when compared the the z80/6502. Maybe it's because there aren't any suppliers of new chips? But it's a super platform with the serial ports built in - great option for a little retro computer board.

 

[norwestrzh]

Yes, Plasmo, it is an 18.432 oscillator. I didn't try anything faster because the SRAM is marked 55 n.s.

Good to know that it might be able to be powered from USB, bsd64. If you play around with the Z180, you'll soon learn that the on-chip serial is a bit "funky". The IN/OUT opcode using the C register as the port address doesn't work quite the same as with the Z80. There are good reasons for that. The Z180 was billed as compatible with the Z80, but lots of Z80 applications used those opcodes. They would have to be revised or re-written to work with the Z180. Maybe that's one of the reasons that the Z180 never really "took off"???

Roger