Schweitzer Engineering Laboratories SEL-587Z - SEL Distributed Port Switch Protocol (LMD)

6.10
SEL-587Z Instruction Manual Date Code 20020903
Serial Port Communications
SEL Distributed Port Switch Protocol (LMD)
SEL Distributed Port Switch Protocol (LMD)
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 1 or SET P F
command to activate the LMD protocol. Change the port PROTO setting from
the default SEL to LMD to reveal the following settings:
Operation
The following explains the operation of the LMD protocol:
1. The relay ignores all input from the port selected to the LMD
protocol until it detects the prefix character and the two-byte
address.
NOTE: You can use the front-panel
{SET} pushbutton to change the port
settings to return to SEL protocol.
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 PROTO = 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.
Setting Description
PREFIX One character to precede the address. This should be a character which 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.