Guralp Systems CMG-DCM User Manual

Page 85

Operator's guide

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.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.dss : If you have set the serial.x.service option to

dss_sum, this

option lists the DSS data types that will be transmitted. If the port is
not running the

dss_sum service, this setting will be ignored.

serial.x.ppp : If you have set the serial.x.service option to

ppp, the

DCM will use the standard Linux command pppd to manage the PPP

service for this port. The serial.x.ppp option allows you to add
command-line options to pppd which are specific to this port. The

command-line options are fully described in the Linux documentation

for pppd.

If the port is not running the

ppp service, this setting will be ignored.

Any options which apply to all serial ports running the

ppp service

should be placed in the /etc/ppp/options file instead (see Section

serial.x.ack_nak_timeout : If you have set the serial.x.service option to

gcf_out, this option sets the length of time, in milliseconds, that the

DCM will wait for a response to each GCF block sent from this port,
before giving up and sending the next one.

December 2006