Date Code 20011205
M
IRRORED
B
ITS
Communications
H-1
SEL-311A Instruction Manual
APPENDIX H: M
IRRORED
B
ITS
™ COMMUNICATIONS
O
VERVIEW
M
IRRORED
B
ITS
is a direct relay-to-relay communications protocol that allows protective relays
to exchange information quickly and securely, and with minimal expense. The information
exchanged can facilitate remote control, remote sensing, or communications-assisted protection
schemes such as POTT, DCB, etc. The SEL-311A supports two M
IRRORED
B
ITS
channels,
differentiated by the channel specifiers A and B. Bits transmitted are called TMB1
x
through
TMB8
x
, where
x
is the channel specifier (e.g., A or B), and are controlled by the corresponding
SEL
OGIC
control equations. Bits received are called RMB1
x
through RMB8
x
and are usable as
inputs to any SEL
OGIC
control equations. Channel status bits are called ROK
x
, RBAD
x
, CBAD
x
and LBOK
x
and are also usable as inputs to any SEL
OGIC
control equations. Further channel
status information is available via the
COM
command.
Important:
Do not connect an unconfigured port to a M
IRRORED
B
ITS
device. Otherwise the
relay will appear to be locked up. Configure the port first, then connect the device.
O
PERATION
Message Transmission
All messages are transmitted without idle bits between characters. Idle bits are allowed between
messages.
·
At 4800 baud, one message is transmitted each 1/2-power system cycle.
·
At 9600 baud, one message is transmitted each 1/4-power system cycle.
·
At 19200 and 38400 baud, one message is transmitted each 1/8-power system cycle for
the SEL-321 and 1/4 power system cycle for the SEL-311A.
Message Decoding and Integrity Checks
The relay will deassert a user-accessible flag per channel (hereafter called ROK
x
) upon failing
any of the following received-data checks:
·
Parity, framing, or overrun errors.
·
Receive data redundancy error.
·
Receive message identification error.
·
No message received in the time three messages have been sent.
Summary of Contents for SEL-311A
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