Date Code 20110408 Instruction Manual SEL-551 Relay
Appendix C
SEL Distributed Port Switch Protocol
Overview
SEL Distributed Port Switch Protocol (LMD) permits multiple SEL relays to
share a common communications channel. It is appropriate for low-cost, low-
speed port switching applications where updating a real-time database is not a
requirement.
Settings
Use the front-panel {SET} pushbutton or the serial port SET P command to
activate the LMD protocol. Change the port PROTOCOL setting from the
default SEL to LMD to reveal the following settings:
Operation
1. The relay ignores all input from this port until it detects the
prefix character and the two-byte address.
2. Upon receipt of the prefix and address, the relay enables echo
and message transmission.
3. Wait until you receive a prompt before entering commands to
avoid losing echoed characters while the external transmitter is
warming up.
4. Until the relay connection terminates, you can use the standard
commands that are available when PROTOCOL is set to SEL.
Setting Description
PREFIX: One character to precede the address. This should be a character that
does not occur in the course of other communications with the relay.
Valid choices are one of the following: “@” “#” “$” “%” “&.” The
default is “@.”
ADDRESS: Two character ASCII address. The range is “01” to “99.” The default
is “01.”
SETTLE TIME: Time in seconds that transmission is delayed after the request to send
(RTS line) asserts. This delay accommodates transmitters with a slow
rise time.
NOTE: You can use the front-panel
{SET} pushbutton to change the port
settings to return to SEL protocol.
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