Westermo MRD-310, Reference Manual

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3.4.2 CSD Multiplexed
The Circuit Switched Data (CSD) Multiplexed mode allows any
one of the available MRD-3xx serial ports to be selected at
the time of connection. This is achieved through having a vir-
tual console to which the initial connection is made. The caller
can then issue a command to select a port. Once selected, all
data will be directed to the port.
Multiplexed mode can be configured to have a default port.
This port will be selected should no connection command
have been received within a specified time period or a number
of bytes have been received.
A disconnection sequence can be described which when
received by the MRD-3xx will disconnect the serial port cur-
rently selected and return the connection to the virtual termi-
nal. Another port can then be selected, allowing communica-
tion with multiple devices in one CSD telephone call.
The virtual terminal can operate in a verbose mode which
will send prompts and echo characters sent to it. This mode is
best used when issuing the commands manually as it provides
the user with feedback. Alternatively the virtual terminal can
operate in silent mode returning no character to the connec-
tion. This mode is best used when doing a machine-to-machine
type connection, where spurious character could cause prob-
lems.
The command used to select the required port is:
PORT=x\r
where x is the number of port and \r is a carriage return
(0x0d ASCII) . No spaces should be present within the com-
mand string and the command.
The disconnect string is of the form:
<guard time><disconnect character><disconnect
character><disconnect character><guard time>