Texas Instruments 980A

The arrival of the 980A spelt the end for the old Elliott and IBM computers. Because of the greater ease with which minicomputers could be expanded/connnected to other equipment, they were the perfect choice for an engineering environment.

Originally, just the base 980A computer was purchased, and an old paper tape reader and printer were attached so we could become familiar with the system.

Later,a Diablo disk pack storage drive was added, and this allowed all the paper tapes to be put on disk and the tape reader taken out of service. The Vista display terminal was also liberated from the old 803 computer and attached.

An 8 inch floppy disk drive was also attached, as the disks were becoming increasingly popular. No suitable disk controller was available, so a custom controller was designed and built from 7400 series TTL chips. The implementation required a lot of them !

In the photos below, the large display screen with lightpen was called IDIIOM (short for "Information Displays Incorporated Input Output Machine)". It was donated by another department, but unfortunately they wanted to keep the Varian 620/i computer it was equipped with. However the IDIIOM was well documented and it was not too difficult to interface it with the 980A.

As I didn't have the Varian computer and its associated software, everything required to make use of the IDIIOM had to be coded from scratch, including the search algorithm to detect and follow the lightpen around the screen.

The circuity of the IDDIOM was complex, being a mix of analogue and digital electronics, much of the analog circuitry being implemented in proprietary hybrid modules.

At one time, it failed because of a problem with one of these modules. Unfortunately no spares were available. So the faulty module had its lid carefully removed, and after close inspection a broken connection was found. Following surgery under a microscope with the smallest soldering iron bit I could locate, the problem was fixed. Everything worked again !

The IDDIOM is shown here running a rudimentary program I created to assist with printed circuit board design.