95% Chimp

My original plan for the LINK_01... my first homebrew computer... was to ultimately have it built using a single PCB. But the more I think about that decision and the limits that would impose on the machine the more I want to go another direction. I'm heavily influenced by the RC2014 Z80 based homebrew machine which has been going since 2013... and the backplate design which the RC2014 uses goes right back to the birth of home computers. Breaking a machine down into discreet modules and making them all connect to a standard connector is a great way of managing both development and post-launch expansion. As long as the backplate supports enough signals so that you don't limit yourself the sky is literally the limit. The extra connection length may mean that you can't crank the speed up quite as high as a single-PCB machine, but maximum performance isn't something I'm aiming for with this machine... I just want to get something working which I can build upon. I'm ...

 I'd like to write some pithy blog articles about what I've been up to with the old electronics but I've not got the energy so I'm just going to post some pictures instead... here goes... My first actual circuit that does something. This one drives a simple 1BPP VGA monitor signal using a few pins on a Pi Pico. First shot of the LINK_01 BBC (BreadBoard Computer)... Here we have the Pico, which is in control of the whole thing, the VGA out, a bank of 3V3 to 5V voltage shifters and a bank of bi-directional shift registers, which I plan to use for letting the Pico read and write to RAM. There's a 65C02 up there too, buried behind my debug LED bank. Initial work on adding the busses to the design. 16 bit address, 8 bit data and whatever else I think is worth bussing. Now with added 8K EEPROM and RAM... I think it's the old 8K RAM I started with which has now been swapped out for a 32K one. You can see the bus sea-monstering it's way across the breadboards... I g...

 It's now up on archive.org for anyone who wants to read it. HERE