CMG-DCM
The stand-alone DCM has three RS232 serial ports brought out on 10-pin mil-
spec connectors, labelled PORT A, PORT B and DATA OUT. The labelling is
provided for convenience, and can be ignored if it does not match your site
requirements: each port may be used for communication in either or both
directions.
Each serial port has its own configuration screen, with a number of options
beginning serial.x (where x is the internal number of the serial port). The
configuration options for all the ports are as follows:
serial.x.baudrate : This option alters the speed of communication across each
serial link, in bits per second.
For ports connected to digitizers, you should ensure that the baud rate is high
enough to allow all the data to be transmitted at the rates you have chosen. As
an example, for three streams transmitting at 100 Hz, a rate of 9600 baud is
usually sufficient. Modern modems can normally operate at rates up to 57600
baud (~56 kbits/s), although the telephone or transmission lines may not support
such a high rate. The same is true of radio telemetry links.
The DCM's serial ports operate using frames of 8 data bits, no parity bits, and
one stop bit.
serial.x.device : The pathname of the Linux device corresponding to this serial
port. You should not need to change this option.
serial.x.handshaking : The flow-control (handshaking) protocol used across
each serial link. There are three options:
•
off : Transmit data across the serial link without handshaking, i.e.
assume that the link is always ready to send or receive data.
•
rts/cts : Use the Ready To Send/Clear To Send handshaking method,
where two separate lines within the serial cable are used to control the
flow of data. This is the most reliable method since accomplished in
hardware, but is not feasible for long-distance or complex connections.
•
xon/xoff : Send the two special characters
^Q
(17) and
^S
(19) as part of
the data stream to request that data transfer be started and stopped. This
method requires only a single connection, but assumes that the special
characters will be received correctly every time.
serial.x.name : The name of this serial port. You should not ordinarily change
this setting.
serial.x.ppp : You can use any of the serial ports to establish a network
connection with a computer using the PPP protocol by setting the
serial.x.service option, below, to ppp. The DCM uses the standard Linux
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Issue A
