Hi
I have just remembered how the later version keyboards worked.
It was still a counter sytem but the values where fully decoded.
It worked on a matrix system.
Each key on the keyboard sat across the junction of one of the matrix
points.
The columns, say 16. Would be the output of a 4 in 16 out decoder and
the rows were the
inputs of a say 16 in four out encoder. Stopping the clock by pressing a
key gave you an 8 bit keycode.
Serialize in the usual way.
Finally dedicated chips appeared. But same old matrix system.
Rod Smallwood
-----Original Message-----
From: cctech-bounces at
classiccmp.org
[mailto:cctech-bounces at
classiccmp.org] On Behalf Of Ethan Dicks
Sent: 22 May 2007 13:58
To: General Discussion: On-Topic and Off-Topic Posts
Subject: CiTOH terminals (was Re: Well,now I've gone and done it...
Dragged home more big(ish) iron...)
On 5/22/07, Mr Ian Primus <ian_primus at yahoo.com> wrote:
The 101 is the model shaped and colored much like
a VT100. The
keyboard looks similar... but its protocol is _not_ compatible with
the VT100.
Good thing I didn't buy the one on eBay a couple months ago. There was
a 101 there, and cheap too, but it had no keyboard.
I may haev a few CiTOH terminals to drag to VCFmw if there's any
interest. Closer to the event, I'll inventory what I have and see if I
kept any spare keyboards "just in case", if anyone out there already has
a terminal, but can't figure out why their VT100 keyboard doesn't work
with it.
I remember back in the day, since we had dozens of CiTOH and DEC
terminals, looking over the available schematics for both and not being
able to figure out how the keyboard works. I think it was a matter of
inadequate/fuzzy docs more than anything else. Does anyone know of a
good printset to pore over to see the nuts-and-bolts of a VT100-era
keyboard? ISTR the crux of it was a 6402-type UART squeezing out the
keystrokes at some slow baud rate, but I can't recall any essential
details right now. I'm just curious if it's possible to swap a crystal
or make a simple, switched change to allow one keyboard to work across
both vendor's product lines.
We used to have lots of dead keyboard when there was one or two
terminals on everyone's desk. Since the company was shrinking at that
stage, we never bothered fixing them - we just pulled one off a vacant
desk and kept working. The number of working keyboards never shrank
below the steadily decreasing size of the staff, so economically, it
made sense. I think I only saved working keyboards in that set of 4 van
loads, but it's entirely possible I picked up one or two dead ones.
Right now, I have to search the pile for a VT100 keyboard to get my
DECmate I back up and running so I can press it into service as an
RX01/RX02 image archiver and finally whittle down my cartons of
floppies.
-ethan