Racal Vadic modem switch settings

[Rich Altmaier]

Regarding mail from Lauren on Racal Vadic modem settings.

It is recommended the data rate switch be set to 1204 bits/sec.
We have found some terminals dialing up to Unix (Vax, Berkeley 4.1)
get garbage data when continuous 1200 baud transmissions occur from the
computer.
I have found this is due to the RV modem's clock being slightly slower
than the source of RS232 signal from the computer.  It is not unreasonable
for there to be a small percent difference.  However if continuous
transmissions occur from the computer, then the modem gets steadily
behind as it has to assemble each character and re-serialize it
(encoding in 212, bit pair codes).  After about a 100 chars we would
get a character transmisson from the modem aborted (bits dropped), immediately
followed by the next char.  This would be just one bad char except
with continuous transmission, the receiving modem is now out of sync
(it thinks it finds start bits in the middle of chars, etc).

A Racal-Vadic rep told me the way Bell modems deal with this is to
drop stop bits to allow it to catch up.  The RV modem just aborts
a character.  The RV solution is the data rate switch.  Change it to
transmit at a slightly higher rate (our VA3480 can set to 1219
bits/sec, 1.6% fast).  Then it has no problem keeping up with a slightly
higher (< 1.6%) RS232 feed.

-------------
We have encountered the same(?) bug as mentioned by Lauren where the
modem holds the line off hook emitting a garbage stream out the RS232 line.
Our chassis mounted VA3480
modems have switch option:
    A-6 ON=Dialers- Unattended disconnect,
	   disconnects modem fromline when phone is placed on hook.
	OFF=No Dialers- connects modem to line when phone is placed on hook.

This description makes no sense to me, but then the whole manual is
fairly obscure.  Is this the same option as you recommended setting
to Off (Unattended)?

	Rich Altmaier
	Integrated Office Systems 408 257-0171
	{decwrl|oliveb}!ios!richa