Managing the Radio | 133
Aprisa SRi User Manual 1.1.0
Mirrored Bits®
This menu item is only applicable if the serial port has an operating mode of Mirrored Bits.
Introduction
Mirrored Bits® is a serial communications protocol used to exchange internal logic status messages directly
between relays and devices used in line protection, remote control and monitoring, relay remote tripping,
sectionalizing and other such applications.
The protocol relies on near constant transmission of status bytes between the devices. It can only tolerate
small delays between receipts of packets.
The protocol provides alarms states to monitor and report on radio channel performance. If a receiving
device does not receive a status packet within a pred
efined time then it asserts an ‘
instantaneous channel
monitor
’
error (ROK), this error clears as soon as the next status packet is received.
There are two more significant errors RBAD (ROK dropout for settable time) and CBAD (long term channel
unavailability exceeding a settable threshold) that will be asserted if more extensive delays occur or the
communications channel is lost.
The trigger or time period for asserting ROK varies between devices. Typically, the ROK error state is
asserted if a receiving device does not receive a packet for a period > than 3 x the period taken to transmit
a packet.
When optimizing for Mirrored Bits® operation, the target is to present a radio channel that does not result
in ROK triggers occurring. Individual networks may be tolerant to occasional ROK alarms states if configured
to make use of the more significant alarms.
