G.4
SEL-2414 Transformer Monitor Instruction Manual Date Code 20130214
MIRRORED BITS Communications
Overview
In summary, when a device detects an error, it transmits an attention message
until it receives an attention message with its own TX_ID included. If three or
four devices are connected in a ring topology, the attention message will go all
the way around the loop until the originating device receives it. The message then
dies and data transmission resumes. This method of synchronization allows the
devices to reliably determine which byte is the first byte of the message. It also
forces unsynchronized UARTs to become resynchronized. On the down side, this
method takes down the entire loop for a receive error at any device in the loop.
This decreases availability. It also makes one-way communications impossible.
Loopback Testing
Use the LOOP command to enable loopback testing. In the loopback mode, you
loop the transmit port to the receive port of the same device to verify transmission
messages. While in loopback mode, ROKc is deasserted, and another user acces-
sible Device Word bit, LBOKc (Loop Back OK) asserts and deasserts based on
the received data checks (see the Section 7: Communications for the ASCII com-
mands).
Channel Monitoring
Based on the results of data checks (described above), the device collects infor-
mation regarding the 255 most recent communications errors. Each record con-
tains at least the following fields:
➤ DATE—Date when the dropout occurred
➤ TIME—Time when the dropout occurred
➤ RECOVERY_DATE—Date when the channel returned to service
(if the channel is currently failed, it is displayed and included in
the calculations, as if its recovery were to occur at the time the
report was requested)
➤ RECOVERY_TIME—Time when the channel returned to service
(if the channel is currently failed, it is displayed and included in
the calculations, as if its recovery were to occur at the time the
report was requested)
➤ DURATION—Time elapsed during dropout
➤ CAUSE—Reason for dropout (see Message Decoding and
Integrity Checks on page G.2)
There is a single record for each outage, but an outage can evolve. For example,
the initial cause could be a data disagreement, but framing errors can extend the
outage. If the channel is currently failed, it is displayed and included in the calcu-
lations, as if its recovery were to occur at the time the report was requested.
NOTE: Combine error conditions
including RBADA, RBADB, CBADA, and
CBADB with other alarm conditions
using SEL
OGIC control equations. You
can use these alarm conditions to
program the device to take
appropriate action when it detects a
communications channel failure.
When the duration of an outage on Channel A or B exceeds a user-definable
threshold, the device asserts a user-accessible Device Word bit, RBADA or
RBADB. When channel unavailability exceeds a user-definable threshold for
Channel A or B, the device asserts a user-accessible Device Word bit, CBADA or
CBADB. Use the COMM command to generate a long or summary report of the
communications errors.
Use the RBADPU setting to determine how long a channel error must last before
the meter element RBADA is asserted. RBADA is deasserted when the channel
error is corrected. RBADPU is accurate to ±1 second.
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