serial printer problem on 3b2-600

[Leslie Mikesell]

In article <506 at mtndew.Tustin.CA.US> friedl at mtndew.Tustin.CA.US (Steve Friedl) writes:
[XOFF skid on 3B2 EPORTS...]
>     At 19200bps it is reportedly 16 or 32 character times (don't
>remember which), and for some devices -- the HP LaserJet comes to
>mind again -- this is just too much.  The only solutions are to
>slow down the printer, use hardware flow control, or get a real
>computer like an NCR Tower :-).

Another way that should work would be to add one of those serial buffer
boxes that are commonly used between PC's and printers.  They can
be found for <$100 in the smaller buffer sizes, which should be cheaper
than dumping the computer (at least in the short run). 

>     To really do this right would require that the UART have
>special "watch" character so it would issue an interrupt if the
>mentioned character arrived in the port.  Then the onboard CPU
>could do scanning as usual with occasional forays to service a
>port that just got XOFFed.  Alas, this wasn't done on EPORTS.

No, to do it right the on-board CPU should have sufficient capacity
to service the received character interrupt from the UARTs under
all conditions.  Micro-CPU's are not prohibitively expensive for
this.

[...software/hardware flow control are mutually exclusive]

>    If anybody out there knows of ANY reason why this is the
>case, even a bad reason, I would love to hear it.  I want very
>much to believe that AT&T is not full of sh*t, but so far that's
>the only conclusion I'm able to come to. 

Well they do have that reputation to maintain.

Les Mikesell
  les at chinet.chi.il.us