Interesting, I thought TTL didn’t like voltages that were too negative but I’m definitely not too great on the historical stuff. This data sheet for 7400 logi

Interesting, I thought TTL didn’t like voltages that were too negative but I’m definitely not too great on the historical stuff. This data sheet for 7400 logic, which admittedly only goes back to 1983, doesn’t like inputs below -1.5V That could very likely be because ESD protection was added and 1970 TTL parts didn’t have that. https://www.jameco.com/jameco/products/prodds/910901.pdf https://www.jameco.com/jameco/products/prodds/910901.pdf