Delving into VersaLOGIC's Pre-LSI Logic Cards, specifically focusing on the Data/620 model.
In an exciting development, David Lovett's reverse-engineering efforts for the VersaLogic cards are now publicly available on GitHub [1]. These cards, which were once used at NASA, are a fascinating relic of the 1960s computing era.
David is currently working on troubleshooting the Data/620 machine, a 1960s computer containing hundreds of VersaLogic cards. The goal is to restore this historical machine to working condition.
The VersaLogic cards use high-threshold logic (HTL) with -12- and 0V, a technology that requires specific testing methods. Unfortunately, there are no direct search results specifically addressing how to test HTL circuits on VersaLogic cards from the 1960s. However, based on general knowledge of HTL circuit testing and vintage logic cards, testing typically involves providing appropriate input voltage levels above the HTL logic threshold and measuring output signals with an oscilloscope or logic analyzer.
To test these vintage cards, one would need to:
- Power the card with the specified HTL voltage supply (check documentation for exact voltages, commonly +15 V or +24 V).
- Apply known test input signals at voltages above the HTL high-level threshold and below the low-level threshold.
- Use an oscilloscope or logic probe that can handle the higher voltage levels to observe logic transitions on the outputs.
- Verify switching thresholds and propagation delays against original datasheets or manuals if available.
- Use continuity and resistance measurements to rule out damaged components.
Given the complexity of some of the circuits on the VersaLogic modules' cards, this process can be challenging. As such, detailed manuals or testing circuits from that era would be critical. Modern sources rarely cover such niche legacy equipment testing directly, so vintage computer restoration forums, vintage electronics documentation archives, or contacting museums and collectors that specialize in 1960s logic hardware may provide invaluable resources.
Meanwhile, David Lovett has two examples of modular and reusable logic circuits from the 1950s and 1960s at the Usagi Electric farm. The Usagi Electric community is also working on the VersaLogic cards' reverse-engineering, and their Discord channel is open for collaboration.
Interestingly, the newer Varian Data Machines 620 from 1966 has more than double the logic on similarly sized cards compared to the Bendix G-15 from 1956. Despite this, the Bendix G-15 effectively fulfills the same purpose as the transistors in the Varian Data Machines 620, albeit with the aid of germanium diodes and vacuum tubes. The Varian Data Machines 620 also has a significantly reduced power usage compared to the Bendix G-15.
As David's work continues, it offers a unique opportunity to delve into the history of computing and understand the evolution of technology from vacuum tubes to transistors and beyond.
[1] GitHub link: https://github.com/DavidLovett/VersaLogic-reverse-engineering
References: - GitHub link: https://github.com/DavidLovett/VersaLogic-reverse-engineering
- To fully grasp the testing process for the VersaLogic cards, it would be beneficial to refer to the data-and-cloud-computing literature on high-threshold logic circuit testing, as well as consult with resources related to vintage logic cards.
- As David Lovett's work progresses on the VersaLogic cards, he is not only restoring a piece of hardware from the 1960s, but also contributing to the wider field of technology and computing history.
