R.9.26
SEL-421 Relay Reference Manual Date Code 20111215
ASCII Command Reference
Description of Commands
LOOP
The LOOP command puts the relay serial port in loopback if you have
previously configured the port for M
IRRORED BITS communications. If you
have enabled both of the M
IRRORED BITS communications channels (A and
B), then you must specify the channel parameter. If you have only one of the
channels enabled, then the relay assumes that channel if you do not specify
that channel in the command. If you do not specify a timeout period, the relay
provides a 5-minute timeout.
You can enter the options in any order. If you operate the relay using both
M
IRRORED BITS communications channels (A and B), then you must specify
the channel parameter by using the LOOP A command and the LOOP B
command.
When you issue the LOOP command, the relay responds with statements
about the loopback time, status of the RMB (Receive M
IRRORED BITS), and
Are you sure (Y/N)? If you answer Y <Enter>, the relay responds,
Loopback Mode Started.
In the loopback mode, ROK drops out and the relay uses LBOK to indicate
whether the data transmissions are satisfactory. The relay collects COM data
as usual. Time synchronization and virtual terminal modes are not available
during loopback. The relay continues passing analog quantities.
LOOP DATA
The LOOP DATA command tells the relay to pass input MIRRORED BITS
communications data through to the receive (RMB) bits, as in the
nonloopback mode.
Table 9.68 LOOP Command
Command Description Access Level
LOOP Begin loopback of a single enabled MIRRORED
B
ITS communications channel (either Channel A
or Channel B) for 5 minutes; ignore input data
and force receive bits (RMB) to defaults.
P, A, O, 2
LOOP c
a
a
Parameter c is A or B, representing Channel A or Channel B.
Begin loopback of MIRRORED BITS communica-
tions channel c for 5 minutes; ignore input data
and force receive bits (RMB) to defaults.
P, A, O, 2
LOOP t Begin loopback of a single M
IRRORED BITS
communications channel (either Channel A or
Channel B) and end the loopback after timeout t
minutes; ignore input data and force receive bits
(RMB) to defaults; t range is 1–5000 minutes.
P, A, O, 2
LOOP t c Begin loopback of a single M
IRRORED BITS
communications channel (either Channel A or
Channel B) and end the loopback after timeout t
minutes; ignore input data and force receive bits
(RMB) to defaults; t range is 1–5000 minutes.
P, A, O, 2
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