Re: Dynalink modem/Super serial combo

[dempson@atlantis.actrix.gen.nz (David Empson)]

In article <4glopj$3e4@nyx.cs.du.edu>,
Will Baguhn <wbaguhn@nyx.cs.du.edu> wrote:
> In article <8BB2530.0217001EA6.uuout@powerlink.iconz.co.nz>,
> GRAEME WILLIAMS <graeme.williams@powerlink.iconz.co.nz> wrote:
> >
> >I have purchased a 14400 Dynalink modem model 1414vqe, which is a plain
> >14400 bps modem with v.32....
> >I have connected it to a stock Apple super serial card...
> >
> >I can control the modem by typing stuff like ATM1, ATDT xxxx etc and
> >that works ok, but it doesn't echo or return anything to my 2e. It's
> >getting a bit dull trying to imagine what should be on screen :-)

There is a very good reason for this: the Super Serial Card will not
receive anything from the modem unless the Carrier Detect signal (pin
8) is active.  Most current modems default to AT&C1, which tells the
modem to activate Carrier Detect when a connection is established.
Before you connect, you will not receive anything.

To avoid this, your options are:

1. Use &C0 in the initialization string.  This tells the modem to
   leave carrier detect active all the time.  The disadvantage is that
   this will prevent the software from detecting a lost connection.

2. Disconnect the wire providing the Carrier Detect signal to the computer
   (pin 8) - same result.  The Super Serial Card will assume that the
   carrier is always present.

3. Rewire the cable to provide the Carrier Detect signal to the Super
   Serial Card via a different pin, e.g. pin 6 (Data Set Ready) which is
   not normally used.  If the software supports this remapping, it will
   be able to detect a lost connection by monitoring DSR instead of DCD.

> i had a similar problem with my //e, SSC, and intel 144/144e.
> 
> what i finally did was turn the jumper block on the SSC to point to
>  "printer", and install a null modem between the modem and the SSC.

This is probably a side effect of the null modem cable.  The jumper
block set to TERMINAL rearranges the signals so that the DCD signal is
provided from pin 4 (RTS), which is also looped back to pin 5 (CTS).
If the null-modem cable just swapped RTS and CTS back, then the
modem's CTS signal will be fed into the carrier detect input of the
6551 chip.

You won't be able to do hardware handshaking with this arrangement.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand