| Steve:
I'm no expert, but I'll give an early answer and hope that some-
one else comes along to give you a definitive answer.
The LK201 and LK401 are electrically compatible. The signalling
is via that 4-pin modular "handset" connector, using +12 and ground
and RS232 transmit and receive data leads at 4800 bits/second.
The proof of this compatibility is that later terminals (and my
VAXstation) can use either an LK201 or LK401 interchangeably.
"Keyboard Error 4" is the standard message you get when there's
no keyboard attached. I'd *GUESS* that what's really happening
is that the VT220 is trying to read some sort of ident from
the keyboard and the LK401 either doesn't respond to the VT220
at all (unlikely) or it responds with an ident that the VT220
wasn't prepared for, and the VT220 concludes that this device
isn't a keyboard.
As I said, I hope an expert comes along soon to answer definiti-
tively. Otherwise, you could kludge a datascope into the terminal
cable and look for yourself. You might also ask in KEYBOARD_DESIGN.
Atlant
|
| This keeps coming up in some form or other. I guess this
is a good place to record a few facts.
Yes, electrically identical. The 401 powers up in 201 mode,
and usually works wherever a 201 would.
There is 1 "gotcha"; the 401 can't handle the same data rates
as the 201 could. The protocol always included ACKs for certain
commands. You're not allowed to have more than one ACKed
command outstanding. The 201 was fast enough that as a
practical matter, some products ignored the requirement, but
worked. With the 401, same code didn't. (Note this has to
do with how fast bytes of data are sent, not the line signaling speed
in bits per second. The latter is fixed at 4800.) Some of the VAX
workstations had ROMs/drivers which fell into this.
As for IDs, the 401 reports it is a 201. It is possible to tell
them apart, but the 401 didn't change the originally-specified ID
field in order to provide compatibility.
I don't know if the 220 firmware(s) played by the rules, though
some people have reported success using the 401 with some models.
One other hint: cable lengths matter. Too long (and too short)
can both cause problems.
T
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