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Day 1: taking stock

A project log for Detritus, the 8-bit ... computer?

I have a lot of random spare parts doing nothing and a need to make them do things...

jorj-bauerJorj Bauer 05/19/2017 at 01:320 Comments

My plan here is to do this build primarily at work, during my lunch hour. To do that, I need some idea of what I'm building; and a reasonable set of parts out of which to build that thing.

Well, I know what I want to build, sort of. The recently popularized Ben Eater 8-bit computer videos made me think about building something similar. So that's easy. Ish.

But what, exactly, do I have? Well, here's some of it. The static foams are loaded on both sides with ICs...

Ignoring the families (many of these are TTL; some are the LS family, and others are not; some are CMOS; etc.) -- and just cherry-picking the parts that look interesting and possibly useful:

6x 7400 quad 2-input NAND gates

1x 7402 quad 2-input NOR

5x 7404 hex inverter

5x 7405 hex inverter

1x 7406 hex inverter

1x 7407 hex inverter

1x 7408 quad 2-input AND

1x 7410 triple 3-input NAND

1x 7420 dual 4-input NAND

1x 7421 dual 4-input AND

1x 7448 BCD to 7-segment driver

2x 7427 triple 3-input NOR

1x 7483 4-bit adder w/ fast carry

2x 7432 quad 2-input NOR

1x 7490 decade counter

1x 74135 1-of-8 decoder

2x 74138 1-of-8 decoder

3x 74139 dual 1-of-4 decoder

7x 74173 4-bit d-reg tri-state

3x 7476 dual j/k flip-flop

1x 7474 dual d-type flip-flop

2x DM7446 BCD to 7-seg driver

1x 74174 hex? quad? D-type flip-flop

2x 74153 dual 4-input multiplexer

1x 74193 4-bit up/down counter

1x DM7489 64-bit RAM

1x 74367 hex 3-state buffer/bus driver

1x 74109 dual j/k flip-flop

1x 7475 4-bit bistable latch

2x 74151 1-of-8 selector

1x 74161 4-bit counter

2x 74241 octal tri-state bus driver

1x 74244 octal tri-state bus driver

2x MS6264L-10 static RAM (64k bits)

2x CAT28C64B-20 EEPROM (64k bits)

5x 555 timers

1x 7474 D flip-flop

1x MSM2114 4k static RAM

2x 211A 4k static RAM

6x MC824P quad NOR gates

1x CD4016 quad bilateral switch

1x CD4053 analog 8-channel multiplexer

1x 74157 quad 2-line to 1-line data selector/multiplexer

1x DM8131 6-bit bus equality comparator

... that certainly looks like a good catalog of parts to start with. I'm sure I'll want to order some new parts along the way, but if I use many of those parts that have literally been sitting in my basement for over 20 years, I'll feel like something was accomplished.

Some ground rules for myself, then:

First try to use parts I already have.

If I have to order something, I will - but only the minimum necessary. I want to end this with smaller stockpiles of parts in my basement than when I started.

I would like this to eventually do something interesting. If it only blinks some LEDs, I'll take it. But more is more betterer.

16 protoboards ordered, then! And now it's time to get started.

In Ben's series, he started in a very sane place - the clock. So did I, more or less using his design. Not much to say here; if you want to understand how this works, go watch Ben's videos on the subject. I substituted logic gates that I had lying around, of course; two 7400 series NAND ICs used, along with 3 555 timers. Here it is as the first timer shows that it still works...

It quickly grows, taking on four of the 74173 4-bit registers, making what I think will be an X and Y register. This is more dead-simple read-the-datasheet kind of work and I don't think it needs much description - except to say that I'm a big fan of the 6502 instruction set (my first assembly) and I'm definitely thinking in its terms. Maybe this has too many registers when it's done, but I would like an X/Y and Accumulator...

There's just enough wiring to test whether or not that first (last? rightmost?) register chip still works. So far, so good - no duds in my stock! We'll see where this goes tomorrow, and in a few days I'm expecting a logistical puzzle or two...

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