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A project log for Gigatron I/O and RAM expander

Adding four SPI ports and up to 128K of banked RAM using nothing more than 4 TTL chips and some wizardry.

Marcel van KervinckMarcel van Kervinck 03/26/2019 at 18:552 Comments

I needed some inspiration before resuming with the I/O expander, so this weekend I visited the Vintage Computer Festival in Seattle. 

It's only a 10 hour flight. There are ways to deal with that, such as watching 3.5 movies per leg.

Seattle is a friendly place and great for playing tourist.

The Aquarium is nice too. But why does its restaurant serve fish?

The festival was held at the late Paul Allen's Living Computers Museum + Labs.

Every computer museum must have an Enigma machine of course.

But how many PDP-10's does your museum have in its basement?

PDP units everywhere... Here some PDP-12, PDP-11 and PDP-8 processors and front panels.

When you have a Cray-1 on the main floor just as a visitor's bench, the Cray-2 can sit in storage.

An original Apple 1 that needed some reprogramming. They have three such ultra rare machines on display, but none are even mentioned on the website...

I found Richard Greenblatt and a couple of CADR aka LISP machines in the attic. It's part of what makes it a Living Museum I guess.

How the LISP machine is wired.

And how the Cray-1 is wired.

Richard and a PDP-6 front end, with his Mac Hack Six chess program running in the background.

Part of the VCF show just before opening. You can see my exhibit of two Gigatrons in the center. I only brought one: the Gigatron that I'm using for the I/O expander project. The other I borrowed... believe it or not.... from the museum itself. How bizarre is that.

Driving simulator shootout. All right, we'll call it a draw.

I almost bought this laser videodisc, but it was bundled with the player and I didn't want that.

The result of all of this is a slightly improved version of the LED blinking program. 

It controls 16 LEDs using the following SPI commands to the MCP23S17:

40 00 00 ; Set PORTA to all-output

40 01 00 ; Set PORTB to all-output

40 14 xx ; Send byte value xx to PORTA

40 15 xx ; Send byte value xx to PORTB

Blinking lights are essential for vintage computer shows, especially when your table is next to Oscar Vermeulen's fabulous mini PDP-replicas.

Discussions

Hans wrote 03/28/2019 at 17:40 point

Great post! Thanks for sharing the pictures. Love that PDP collection!

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Richard Hogben wrote 03/26/2019 at 22:23 point

Most entertaining log I've seen in a while :)

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