The IBM 3151 from 1987 is an interesting ASCII terminal. Unlike "normal" serial terminals, it not only supports the so-called "character mode", where after each keypress there is an interaction with the host computer (like with a Unix terminal), but it also has a "block mode". This means, you can send it commands to define fields for input and output on the screen (like a form to fill out). The terminal then handles autonomously all the the user input, and when the user is done and presses a special key (Enter or a function key), all the entries in the form are transferred to the host in one go.

This is very similar but unfortunately not identical to the so-called 3270 terminals used by IBM mainframe computers. Therefore, I wrote a little C program to translate between the differing protocols of 3270 and 3151 terminals enabling a 3151 to be connected to a mainframe.

I made a video describing a little bit the 3151 terminal and the interface program and showing how it looks like to work with the (emulated) mainframe on an 3151. The source code and Windows binary are on github for you to try out, if you happen to have a 3151 terminal. The link is in the description of the video.