Simple Z80 test design - single board with all the basics and a few luxuries. The board has many more options than it really needs so that I can experiment. All devices are through-hole to make the build easy for those of us yet to venture into SMD. Influences for this project include the RC2014 512K RAM/Flash card and the SIO/2 card along with bits and pieces from all over the Internet that I've managed to lose track of.
The paged memory model supports a 4MB address space, 1MB of which is used on board. The main header exports all Z80 control lines plus the extended address bus allowing 3MB external. I'm hoping to add a memory mapped video card along the lines of the 70s/early 80s systems which would sit in the paged memory map. Great for simple games!
The board uses an oscillator chip and an optional divide by 2 to the CPU and SIO. This allows a certain level of exprimentation with clock speeds. I'm using a 10MHz Z80/SIO/CTC and on the first version of the board a 7.35MHz clock. With the CTC it's possible to decouple the system clock from the SIO baud rate so it's easier to play with clock speeds. I'm hoping to use at least a 10MHz clock or possibly higher. I have a 25MHz clock which, with the divide by 2 might work quite nicely. It's also possible to drive the clock externally rather than use the on board one. So I could have a video card with 25MHz dot-clock also driving the main board. Lots of options!
update the board is working nicely and I have it running at 14.7456MHz crystal.
Version 2 board features:
Bug fixes from the version 2.1 board:
Changes from version 1 to version 2
With the SDcard interface working very nicely maybe the board doesn't need 512K of flash. It's a complete PITA to programme compared with simply writing to the SD card. Maybe a smaller flash device?
|11||Resistor SIL x8||RP2,RP3,RP1,RP4||SIL-9||4|
|14||Oscillator 8/14 Pin Layout||OSC||DIP14 - OSCILLATOR||1|
|30||Male Header 2.54mm||PWR||2.54MM_HDR_2PIN||1|