Write up of my homebrew CPU build

P-Nuts a few seconds ago | parent | next [-]

To get both blinkenlights for registers and tri-state for bus driving, use two ’574 chips in parallel rather than a ’377 behind a ’245. Tie the clock and input lines together on both. Tie the output enable low on the one driving the blinkenlights. This way the chip that the rest of the CPU depends on doesn’t have the extra work of driving any load and you only have one chip’s worth of propagation delays.

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komali2 an hour ago | parent | prev | next [-]

> It’s a standalone tool that lives outside the computer. I put the EEPROM into the socket, and connect via serial to my laptop to upload the binary files.

Huh, I guess I never really thought about it, but how did they program the first CPUs? Like how did they overcome the chicken/egg situation?

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moring 41 minutes ago | parent | next [-]

Actual application code was hardwired, entered manually with switches and lights, or with punch cards. Later, when ICs were sufficiently advanced, mask-programmed ROMs/PLAs.

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jacquesm 18 minutes ago | parent | prev | next [-]

Plugboards! Think telephone exchange but used as a ROM.

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b00ty4breakfast an hour ago | parent | prev [-]

I'm going off memory (of a book, not that I was alive in the 40s, ha) so grain of salt etc but I believe the very earliest (edit: electronic, digital) computers were literally rewired every time they need to be re-programmed.

	▲	trq01758 41 minutes ago \| parent [-]
		Yes, check out this https://computerhistory.org/blog/programming-the-eniac-an-ex...

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artemonster 2 hours ago | parent | prev [-]

I always applaud homebrew cpu designs but after doing so many myself I would reaaaaly advice to stay away from dip chips/breadboards/wirewraps and any attempts to put it into real physical world. Taking a build out of a logisim/verilog to real world in chips sucks away all the fun about cpu design - suddenly you have to deal with invisible issues like timing, glitchy half-dead chip, bad wire connection, etc. these are not challenges, just mundane dull work. The only exception to „stay in the sim“ rule is if you want to make an „art statement“, i.e. like BMOW (or my relay cpu https://github.com/artemonster/relay-cpu/blob/main/images/fr... /shamelessplug)

	▲	code_biologist 2 hours ago \| parent \| next [-]
		I'm totally with you personally, but sometimes doing the actually hard part is fun. Type 2 fun. Long ago I took a CPU architecture class and we implemented designs in Verilog as a final project. Apparently people who took the class in the late 90s (before my time) could actually tape-out their designs and pay a few hundred dollars to get fabbed chips as part of a multiproject wafer. I was always curious if those chips actually worked, or just looked pretty.
	▲	moring 2 hours ago \| parent \| prev [-]
		My advice would be to consider the possibility, not necessarily to stay out of the physical world. For some, those physical details may be the fun part. Some hate verilog. Some want to put it on an FPGA, some don't. I, personally, moved away from FPGAs due to bad documentation (looking at you, Lattice). An alternative to Verilog is RTl simulation in a higher-level Language, or even higher-level Simulation. Just remember that you can't define what is "fun".