Date Code 20010521
SEL Distributed Port Switch Protocol (LMD)
C-1
SEL-387E Instruction Manual
APPENDIX C: SEL DISTRIBUTED PORT SWITCH
PROTOCOL (LMD)
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.
S
ETTINGS
Use the front-panel SET pushbutton or the serial port
SET P
command to activate the LMD
protocol. Change the port PROTO setting from the default SEL to LMD to reveal the following
settings:
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 “@.”
ADDR:
Two character ASCII address. The range is “01” to “99.” The default is “01.”
SETTLE: Time in seconds that transmission is delayed after the request to send (RTS line)
asserts. This delay accommodates transmitters with a slow rise time.
O
PERATION
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 in order 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 PROTO is set to SEL.
5. The
QUIT
command terminates the connection. If no data are sent to the relay before the
port time-up period, it automatically terminates the connection.
6. Enter the sequence CTRL-X QUIT <CR> before entering the prefix character, if all relays in
the multidrop network do not have the same prefix setting.
Note:
You can use the front-panel SET pushbutton to change the port settings to return to SEL
protocol.
