This is a log of various changes and progress to the CFT project. This is a long-term project built in my Copious Free Time, hence the name. It's a self-designed, self-built Sixties-style 16-bit mini computer built out of 74xxx integrated circuits. You may be interested in having a look at the full discussion of the CFT computer. This page only documents progress, and it's mostly for myself.
CFT Project Log
The Switch to SMD
I've toyed with this decision a few times in the early days of the project: through-hole components, or surface mount? On the one hand, through-hole components come easier to me, I find routing through-hole boards more natural (pure habit), and well, they look more traditional.
Front Panel Controller Board
I've finally managed to route the front panel controller board. It took a while longer because (shock!) I did pulled yet another 180° turn on the bus layout. I located a cheap(-ish) source for the wire-wrap female headers, which means I can go back to stacking the processor boards together without needing two separate DIN-41662 buses. Instead, the required signals (and only the required signals) travel from board to board via the female headers. This comes at a small cost to board estate, but simplifies a lot of other things, including the processor routing.
First Revision of the Front Panel Guide
More front panel work has been done. There's yet another revision of the front panel artwork and yet another revision of the front panel schematics. I've split the front panel schematics into the two obvious components: one is the front panel controller card that connects to the system bus, and the other is a huge board with all the LEDs, their drivers and their connectors, as well as a the switches, their debounce circuitry, and a tiny amount of logic that only pertains to the front panel itself.
Front Panel Schematic
After far too long, I managed to prepare a first version of the front panel schematic, and it turned out to be a monstrosity, sprawling over seven sheets of A3. Most of the estate is taken by LEDs, current limiting resistors and buffers. There are over 50 ICs on the board, and there's no chance I can route this on the Hobbyist version of Eagle. Thankfully, the design can really be split up into a number of components.
Some examples of CFT Assembly
I finally found some time to make a GeSHI language file for CFT Assembly, and I can share some CFT code here. You might want to have a look at the CFT Programming Guide (on the main CFT page) for an explanation of CFT machine code and Assembly. If you've worked with PDP-8 code, this will look vaguely familiar.
Front Panel Draft
The CFT mini is meant to boot off a ROM (and, eventually, a hard drive), but I find I'm going to need a front-panel very early in the project. It doesn't have to be fancy, and it doesn't have to be complete, but it would help to have the logic in place now. A front panel is good for four reasons:
Major Register Board Routed
After restructuring half the project to add an overflow flag and all the necessary support for it, I got back to routing. I took a much more liberal, placement-centric approach to laying out and routing, and this changed some of the wiring on the buffers to make sure traces don't cross. It makes perfect sense in retrospect, of course, but if you pinswap enough, the number of vias on the board can be reduced a lot. As a result, you get more PCB estate to play with. The result is an elegant looking, clean Major Register board.
