R.5.21
Date Code 20111215 Reference Manual SEL-421 Relay
SEL Communications Protocols
SEL Distributed Port Switch Protocol (LMD)
Set the RX_ID of the local relay to match the TX_ID of the remote relay. In a
three-terminal case, Relay X transmits to Relay Y, Relay Y transmits to
Relay Z, and Relay Z transmits to Relay X. Tabl e 5.1 8 lists the M
IRRORED
B
ITS communications ID settings for Relays X, Y, and Z.
SEL Distributed Port Switch Protocol (LMD)
SEL Distributed Port Switch Protocol (LMD) permits multiple devices to
share a common communications channel. This protocol is appropriate for
low-cost, low-speed port switching applications where updating a real-time
database is not a requirement. The SEL-421 does not have built in LMD
protocol, but you can connect an SEL-421 to an SEL-2885 EIA-232/485
Protocol Converter and connect the SEL-2885 to an EIA-485 multidrop
network. See the SEL-2885 EIA-232 to EIA-485 Transceiver product flyer for
more information on the settings, configuration, and application of the
SEL-2885. (Contact your local Technical Service Center, the SEL factory, or
visit our website at www.selinc.com for a copy of the SEL-2885 product
flyer.)
Initialization
For the first 30 seconds after applying power to the relay, the SEL-2885 listens
for an initialization string from the relay. The initialization string must be
enclosed in square brackets ([ ]). The following table describes the
initialization string fields. To send this string automatically, set AUTO to Y
and append the initialization string to the relay ID setting so that it is included
in the relay power-up header.
Tabl e 5 . 17 M IRRORED BITS Communications Message Transmission Period
Speed in
Bits per Second
TXMODE := NORMAL
MBT := N
TXMODE := PACED
MBT := N
MBT :=Y
38400 1.0 ms 3.0 ms n/a
19200 2.0 ms 3.0 ms n/a
9600 4.0 ms 4.0 ms 7.0 ms
4800 8.0 ms 8.0 ms n/a
Tabl e 5 . 18 M
IRRORED BITS Communications ID Settings for Three-Terminal
Application
Relay TX_ID RX_ID
X13
Y21
Z32
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