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Conference atlant::terminals

Title:Traditional Video Terminals and Monitors
Notice:See 3230 for Sun River information
Moderator:REGENT::LASKO
Created:Tue Mar 18 1986
Last Modified:Thu May 22 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:3256
Total number of notes:14159

3250.0. "vt220 with LK401-AA okay?" by RHETT::SHEPPARD () Mon Feb 24 1997 22:28

Hello,
    A customer recently purchased LK401-AA RevH01 keyboards to upgrade
a number of old VT220 terminals from their original LK201 Rev-AC
keyboards. He now reports that when power-cycled all terminals now
come up again showing the error:
    keyboard error 04
I'm guessing this is an 'unrecognized keyboard' error or something similar.

He double-checked and says the LK201 keyboards still work just fine when
swapped in. Ergo, probably a compatibility issue.

So, two questions:
1. Will an LK401-AA RevH01 play properly with a vt220 ?

2. If not, can anyone shed some light on the physical/electrical interface
   to the LK201 and LK401 keyboards ?

   If the problem is as simple as a pinout-swap, the customer is
   willing to take a stab at fixing it himself -- with the proper info.

Thanks in advance for any pointers or information !


                        Steve Sheppard
                        Digital Unix / Ultrix Applications Support Team
                        sheppard@decatl.alf.dec.com

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3250.1HUMANE::KEYBOARD_DESIGNATLANT::SCHMIDTSee http://atlant2.zko.dec.com/Tue Feb 25 1997 10:0425
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
3250.2Some FactsDOTWRK::LITTTim LittSun May 04 1997 23:3027
    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