These webpages have not been accurately devoid of residence-built computer systems, with all those made on solderless breadboard significantly less repeated, but continue to not rarities. But what is far more of a rarity is this floor-up 8-little bit 74xx logic-based pc (movie, embedded below) with entire supply, an emulator, assembler and exam suite. [JDH] spent a reliable few of months doing the job late into the evening to make this, and the effects clearly show for on their own.
The new JDH-8 is now a figment of truth.
The architecture is a traditional 8-little bit load/retail store microcoded processor with the microcode saved in conveniently programmable AT28C64 EEPROMs for simplicity of tweaking. The deal with bus is 16-bits, which is pretty ample for this, and puts it in line with (admittedly more sophisticated) 8-little bit micros of previous this kind of as the 6502. There is also a hardware stack, and a discrete-logic ALU as effectively! Ultimately, given that that wasn’t plenty of do the job currently, he added in his have discrete logic movie controller.
There are sixteen directions masking memory access, ALU operations and I/O operations. 1 of the wonderful items about this project is that [JDH] conveniently admits the faults designed along the way, and how the architecture didn’t will need to be this complicated. A person example is that components stack wasn’t actually vital as it could just have been carried out in computer software. Also, owing to the implementation, memory accesses were so quick as opposed with the achievable cycle time, that there definitely was no point to using load/retail outlet architecture at all! Continue to, [JDH] experienced entertaining constructing and programming it!
It was interesting to see the use of LogiSim-Evolution to debug first a significant level design of the architecture and then the translation into TTL chips. This scribe wasn’t mindful of that tool (the disgrace!) but is likely to consider this out real before long.
All code for the computer software facet of items can be located on the undertaking GitHub. Potentially the hardware style and design will seem there as very well, be at the time of composing we couldn’t feel to discover it.
Can’t get ample breadboard computer systems? (We just cannot) check this out from previous 12 months. Stuck for a suitable enclosure for your most recent bread breadboard computer? How about a bread bin.
Many thanks [BrightBlueJim] for sending this in!