These pages have not been exactly devoid of household-designed personal computers, with people constructed on solderless breadboard less frequent, but even now not rarities. But what is more of a rarity is this floor-up 8-bit 74xx logic-dependent computer system (video, embedded underneath) with entire source, an emulator, assembler and exam suite. [JDH] invested a solid couple of weeks working late into the night to build this, and the final results present for themselves.
The new JDH-8 is now a figment of truth.
The architecture is a traditional 8-bit load/retailer microcoded processor with the microcode saved in conveniently programmable AT28C64 EEPROMs for relieve of tweaking. The tackle bus is 16-bits, which is quite sufficient for this, and puts it in line with (admittedly extra refined) 8-bit micros of previous these types of as the 6502. There is also a components stack, and a discrete-logic ALU as effectively! Finally, because that was not sufficient perform already, he extra in his individual discrete logic video controller.
There are sixteen directions covering memory access, ALU functions and I/O functions. 1 of the wonderful matters about this challenge is that [JDH] commonly admits the problems designed along the way, and how the architecture did not require to be this intricate. One instance is that hardware stack was not truly necessary as it could just have been executed in computer software. Also, owing to the implementation, memory accesses were so fast compared with the achievable cycle time, that there seriously was no issue to employing load/keep architecture at all! However, [JDH] experienced exciting building and programming it!
It was intriguing to see the use of LogiSim-Evolution to debug first a large stage design of the architecture and then the translation into TTL chips. This scribe was not mindful of that device (the disgrace!) but is likely to check out this out genuine soon.
All code for the software side of things can be located on the task GitHub. Potentially the components style will appear there as perfectly, be at the time of writing we could not appear to be to discover it.
Just cannot get adequate breadboard pcs? (We can’t) check out this out from past calendar year. Stuck for a acceptable enclosure for your most up-to-date bread breadboard computer? How about a bread bin.
Thanks [BrightBlueJim] for sending this in!