The set-up screen is the only part of the code that is written in C and for this I implemented a very minimal windowing like look and feel (the code is nothing to be proud of though and contains lots of repeated code that could be cleaned up).

Writing the code for this terminal really teleported me back to the 1980’s. Luckily with the convenience of quickly erasable NOR Flash memory instead of UV erasable EPROM’s (which would have added 30 minutes or so to every debug cycle).

Setting up the 6845 involves filling in 16 registers so that the 6845 can generate the correct timing signals for the desired resolution. The available data sheets provide more information on how to calculate the needed values. But since that’s a tedious process, I decided to write a small Python application that could calculate those values for me which you can find below and which was surprisingly accurate. Only R7 (Vertical Sync Position) was of a little bit of sometimes and needed a…

The design I came up with probably contains few surprises and is inspired by various designs that are floating around on the internet.

After a long hiatus, which is easily explained as I’ve been working on my most complex project yet. And even more nostalgia I’m afraid… For the last few months I’ve been working on creating an old fashioned video terminal (circa 1980’s) using chips of that era as well (I inherited a ton of TTL chips when my work decided they didn’t need their small electronics lab anymore.). It’s my first digital project in decades and it might still be a bit rough…