The label on the back says BKBDUSWA-002 PR. I am not certain how to parse that. KBD might be keyboard and US the key layout.
The Micro Switch keyboard subassembly is 91SD30-3.
The auction listing didn't say anything more specific about the terminal, either. It did say that everything was working, which perhaps meant that they had access to the rest. Since the keyboard cable has a DB-25 and they said it was RS-232, I was a little bit worried that someone might try to connect it to a serial port. Since I was about 90% sure that a DB-25 meant TTL-level parallel (and likely ASCII), I supposed it would be fried by RS-232 voltage levels. But, in the end, it is fine and indeed still working.
- the space bar and legends on the gray and black keys have yellowed, but the white keys are still bright
- the overall scheme, while not as colorful as some similar keyboards, is still appealing
- the nav cluster is quirky
- CAPS LOCK is stepped, physically locking, and lighted (turns out this is done more or less electrically direct: not even the keyboard's controller is involved)
- some words are spelled out instead of abbreviated, even though they end up wrapped and squeezed, such as FOR-MAT instead of FMT and CALCU-LATE instead of CALC
- but then CTL instead of the standard CTRL (yes, that's what it does even though it's way up there)
- and, finally, ABB-REV
- the power LED is green, still unusual for the early '80s (and still pretty pale)
- most switches are 4B3E, that is, 2.5oz.; but ESC and CTL are 4B6E, that is, 6oz.
- LOCAL is locking, so it's a terminal mode
- these particular switches are still nice and smooth to type on
- the case itself is just plastic
The parallel signals from the DB port of the controller are ordered 6,5,4,3,2,0,1 on the cable. I don't know whether this was due to some constraint of the single-sided PCB layout or because the designer got momentarily confused by the pin mapping of the second half of the 7404 signals (outputs are 2,4,6,8,10,12 for 1,3,5,9,11,13, respectively).
There is a connection for a speaker all the way out to the cable, and what might be a standoff for it on the case, but just a jumper on this keyboard.
The DATA SET READY LED is controlled by a line that also goes (through an inverter) to the external interrupt of the controller. I thought that might mean that not ready (high) would inhibit output, but that doesn't seem to be so. If DSR is toggled after initialization, the keyboard sends some special identification(?) sequence.
Teensy and connector: The LOCAL key sends a different code for lock and unlock (8B and 8C). These codes and the ident string seem to be the only bytes with the high bit set.
The dark keys that don't correspond to ASCII control characters otherwise send ESC codes. Some are compatible with a VT52, such as A, B, C, D for up, down, right, left. All but EXECUTE (ESC i) change when SHIFT is held down. So, ERASE is ESC K and SHIFT ERASE is ESC J, erase end-of-line and erase end-of-screen on the VT52. But INSERT and DELETE are ESC [ I and ESC [ P, as though ANSI escape sequences, except not matching them.