Date Code 20001006 MIRRORED BITS™ I-3
SEL-351 Instruction Manual
In summary, when a node detects an error, it transmits attention until it receives an attention with
its own TX_ID included. If three or four relays are connected in a ring topology, then the attention
message will go all the way around the loop, and will eventually be received by the originating
node. It will then be killed, and data transmission will resume. This method of synchronization
allows the relays to reliably determine which byte is the first byte of the message. It also forces
mis-synchronized UARTs to become re-synchronized. On the down side, this method takes down
the entire loop for a receive error at any node in the loop. This decreases availability. It also
makes one-way communications impossible.
Loop-Back Testing
Use the LOOP command to enable loop-back testing.
While in loop-back mode, ROKx is deasserted, and another user accessible flag, LBOKx will
assert and deassert based on the received data checks.
Channel Monitoring
Based on the results of data checks described above, the relay will collect information regarding the
255 most recent communications errors. Each record will contain at least the following fields:
• Dropout Time/Date
• Pickup Time/Date
• Time elapsed during dropout
• Reason for dropout (See Message Decoding and Integrity Checks)
Use the COMM command to generate a long or summary report of the communications errors.
There is only a single record for each outage, but an outage can evolve. For example the initial
cause could be a data disagreement, but the outage can be perpetuated by framing errors. If the
channel is presently down, the COMM record will only show the initial cause, but the COMM
summary will display the present cause of failure.
When the duration of an outage exceeds a user-settable threshold, the relay will assert a user-
accessible flag, hereafter called RBADx. Note: The user will typically combine RBADx with
other alarm conditions using SELOGIC Control Equations.
When channel unavailability exceeds a user-settable threshold, the relay will assert a user
accessible flag, hereafter called CBADx. Note: The user will typically combine CBADx with
other alarm conditions using SELOGIC Control Equations.
MIRRORED BITS PROTOCOL FOR THE PULSAR 9600 BAUD MODEM.
The user indicates that a Pulsar MBT modem is to be used by responding "MBT" to the RTS/CTS
setting prompt. When the user selects MBT, the baud rate setting will be limited 9600 baud.
Note: The MBT mode will not work with PROTO = MB8A or MB8B.
Courtesy of NationalSwitchgear.com
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