4230/4232/4235 Communications modules
8-5
DIR/
DIAL A/B Downstream time-out
DIR A 200 character periods (or 200ms minimum)
DIR B* 200 character periods (or 200ms minimum)
DIAL A 2000 character periods
DIAL B* fixed 10 second period
If the Comms module receives no response from a downstream
Controller or Comms module for the period of the time-out, it
assumes that the Controller or Comms module has gone off
line. 2000 character periods is approximately 2 seconds at
9600 baud. The longer time-outs provide the delay required to
enable connection of systems over leased line or Internal
Customer Network units.
*The B setting of this jumper imposes the restriction that the
Comms module only polls the first ten Controller addresses:
00 to 09 (if there is more than one downstream Comms
module then it will poll the first ten Controller addresses on
each Comms module: w00 to w09 where w is the address of
the downstream Comms module). Doing this means that the
system is still usable on a slow Comms branch, an Update
System List command not taking too long. However, if you
have Controller addresses greater than 09, you must
remember to put the jumper in the A position.
4
Downstream baud rate selection jumper (JU4): selects the
baud rate for communications downstream of the Comms
module (downstream is labelled B on the Comms module, both
on the connectors and the jumpers). The baud rate selected
applies to both RS232 and RS485, whichever is selected using
jumper 3.
5
Rotary hex switch (ADRS/MODE): used to set the address of
the Comms module (0 to 9) or its type. The first Comms
module in the system, the one connected to the host computer
in a Local Hardware System or the one connected to the dial-
up modem at a remote site, must be set to type F. Subsequent
downstream Comms modules either have their own address (0
to 9) or are set to type E. A Comms module set to type E adds
no address of its own to messages - it simply passes them on.
It can be used to perform RS485/RS232 conversion, or to
extend the physical size of the system for cable lengths greater
than 1km.
6
Upstream transmit and receive LEDs (D17 and D16
respectively): the Rx LED (right hand one of the pair) lights
when the Comms module is polled from upstream; the Tx LED
lights when the Comms module responds by transmitting a
message upstream. (The only time a Comms module will
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