Recreating the Compukit UK101 (3)

Posted on by

After completing the minimal implementation, I expanded the memory using an external static RAM. This modification creates around 40K of usable space – five times more than the “standard” 8K model originally sold. As my soldering had been a little suboptimal to date, I took the opportunity to replace the board I’d made to hold the keyboard socket and video output with one with enough space for socketing the memory chip as well.

Somewhere under the spaghetti of wire is an AS6C1008-55-PCN 1Mbit static RAM chip

My soldering wasn’t quite perfect, as the computer then booted (and hung) with the following message, indicating it was around 8K of RAM light.

Where’s the missing 8K gone?

A quick inspection found that my soldering for the A10 pin on the memory chip AND the wire leading to it from the FPGA were faulty. Soldering iron redployed, and a few minutes later …

Success – 40K of addressable RAM.on a Compukit UK101

One final test – an simple port of the Sunrise and Sunset calculator from Sky & Telescope’s August 1994 edition. On 25th July 2022, sunrise was at 0513 and sunset at 2111 in Derby.

Sunrise and Sunset times in Derby for 25th July 2022