Heathkit ET-3400 Part 1: Designing and building an ETA-3400 Memory/IO Accessory

I received a Heathkit ET-3400 microprocessor trainer from eBay, and I spend some time trying it out. I also design and build an ETA-3400 Memory/IO accessory to go with the trainer, to add a serial port, cassette port, and Tiny Basic to the Trainer. I perform the modifications to the trainer that are necessary to add the expansion connector. The ET-3400 was sold by Heathkit back in the late 70s as an educational device and then later superseded by the slightly newer ET-3400-A in the early 80s. The trainer typically features 256 bytes of RAM, an MC6800 microprocessor, and 1K or ROM. The ETA-3400 memory/IO expansion replaces the RAM with 4K and adds an additional 4K or ROM. For more electronics projects, see http://www.smbaker.com/

Blog Post: https://www.smbaker.com/designing-a-m...
Github Repository: https://github.com/sbelectronics/eta-...