Ye Olde Gigatron and Гигатрон

A project log for Gigatron TTL microcomputer

Just because! A home computer without microprocessor

WalterWalter 08/26/2020 at 15:090 Comments

There's two Gigatron "specials":

Ye Olde Gigatron

The Gigatron was designed to run with old TTL chips. The kits were supplied with modern, CMOS type chips, but the goal was to keep it TTL compatible. Marcel had already started sourcing some old TTL components, most notably an old 70ns SRAM. I've taken over that task, which has led to the creation of what I call "Ye Olde Gigatron". (And yes I know "Ye" was pronounced "The" and the word "Olde" does not exist.)

Not counting the clock and the 75HC595, all the ICs are old. The newest IC on there is the RAM, which is from 1991. All the rest is pre-1990, so over 30 years old!

I've thrown in a mix of stuff:
- 54LS, extended temperature range ("mil-spec")
- 74, standard TTL
- 74S, Schottky
- 74LS, Schottky low-power

Ye Olde Gigatron is a bit unstable and it consumes a whopping 1.2Amps. It requires a good power supply so I used my lab power supply. Also the clock did not work at first. The 74HCT04 provides a clock booster and that started ringing so I had to add a resistor. The clock circuit will not work with Schottky components, so I left in a 74HCT04. A 7404/74H04/.. will not work in a Pierce oscillator design. Still looking into using a 74C04.

The components used are:
6x 74163 (National Semiconductor, 1972)
4x 74157 (Stewart Wagner, 1975)
4x 74153 (Fairchild, 1976)
2x 74283 (Fairchild, 1978)
1x 74S240 (Signtics, 1979)
2x 74S153 (National Semiconductor, 1980)
2x 74S153 (Signetics, 1981)
2x 74S138 (Fairchild, 1982)
3x 54LS377 (Texas Instruments, 1982)
1x 74LS273 (Motorola, 1983)
1x 74LS244 (Signetics, 1984)
1x 74LS153 (Raytheon, 1985)
1x 74LS244 (Signetics, 1986)
1x 74LS32 (Motorola, 1986)
1x 74LS139 (Fairchild, 1986)
1x 27C1024 (ST Microelectronics, 1988)
2x 74LS273 (Texas Instruments, 1989)
1x 62256 (Micron Technology, 1991)

If somebody has older components than this, let me know :-)

2. Gigatronski

Since I gave a talk about the Gigatron at Neuron hackspace in Moscow, I wanted to make a Gigatron with old Soviet chips. Unfortunately, I did not get any from my new Russian friends. By the way, Pavel and others of Neuron Hackspace have a wonderful "Flipper Zero" kickstarter project.
But anyway, after a long time occasionally looking for Soviet TTL chips, I suddenly found Evita, a company in Vilnius, Lithuania, that has a lot of NOS Soviet components. I was able to order everything there. One chip appeared to be broken, but the company send me a replacement at no extra cost.

The chips were new. The newest of the lot is manufactured in 1992 (so strictly speaking, not Soviet but Russian!). They have a different colour than the IC's I'm used to seeing. Also on quite a few, you can see a piece of aluminum on the bottom. I've opened one up, to see that this is used to put the die on before the epoxy is added.

The Soviet chips also have a different pin spacing (2.5mm instead of 2.54mm). But I was able to (gently!) get them all into their sockets, even the larger ones. I did spend quite some time looking for Soviet replacements of the 62256 SRAM and 27C1024 EPROM, but don't believe they ever existed. The 75HC595 is also not available. A Soviet 74LS04 can be found, but it will not work in the pierce oscillator (same as with Ye Olde Gigatron). There is a Societ 74ACT04 version called КФ1594ЛН1, but that is pretty rare and I could not get one. Since it's used for the clock and not the CPU itself, it is not that much of a problem.

I got a white PCB from somebody in Hong Kong, which I used for the Гигатрон. I swapped SRAM in between pictures. It now has the same old SRAM as Ye Olde Gigatron.

Since I ran out of VGA connectors, I bought a cheap one from China, instead of buying from Mouser/Farnell/Digikey, which I've always done for the kits. Although cheap, it also is not as mechanically sturdy and.. quite a bit smaller, so it no longer aligns with the serial connector. Oh well.