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Building a 3270 Terminal Controller

We like to speak about how maximum of our computer systems lately would had been mainframes a scant 40 or 50 years in the past. Because of that, many of us who need to run IBM mainframes such because the IBM 360 or 370 use the Hercules emulator to run the massive iron on their PCs. However, mainframe IBM computer systems used an peculiar taste of terminal and emulating it on a PC isn’t at all times as pleasant. At least, that’s what [lowobservable] concept, so he made up our minds to get a 3270 terminal running with Hercules.

Back within the unhealthy previous days of computing, there have been two primary kinds of terminals. Some firms, for instance DEC, necessarily used terminals as a “glass teletype.” That is, the display used to be an analog of a roll of paper — kind of — and the keyboard straight away despatched issues to the faraway machine. However, firms like IBM and HP liked a unique means. Their terminals handled monitors stuffed with information. The terminal used to be sensible sufficient to mean you can fill in bureaucracy, edit textual content at the display, and you then’d ship all the display in one gulp. Both programs had execs and cons, however — as it’s possible you’ll be expecting — the screen-oriented terminals had been extra advanced.

The challenge became out to be numerous detective paintings. A large number of those previous protocols had been poorly documented and even secret. However, some datasheets for previous interface chips had some main points and eBay even had the chips in query. We had forgotten that the 3270 used 93 ohm coax, however we by no means knew why they picked that exact price.

It turns available in the market had been two other kinds of terminals. One required an excessively subtle controller that did lots of the paintings. The different did lots of the paintings in the neighborhood. Either manner, the mainframe simplest handled the processed information. Luckily, [lowobservable] is documenting what he’s discovered on GitHub.

At the beginning of the challenge, [lowobservable] picked up a surplus terminal unit. However, it had a corrupt disk symbol so it wouldn’t paintings. It did, then again, have a usable diagnostic disk that might communicate to the terminal. This allowed some research of the site visitors which helped resolution some questions.

The finish result’s a controller that isn’t whole (but) however it’s workable. There are plans for an FPGA model that doesn’t depend on out of date chips, too.

Of direction, we want we had an actual IBM 360. You may accept an AS400, even though.