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Diagnostic counters
Bus Message Counter
Bus Communication Error Counter
Bus Exception Error Counter
Slave Message Counter
Slave No Response Counter
Bus Character Overrun Counter
3.8 Exception responses
Exception responses are sent when the slave device cannot handle the query. The format
of an exception response to a master's query is as follows:
01 ILLEGAL FUNCTION
02 ILLEGAL DATA ADDRESS
20 Modbus function codes ç RVT communication
The total number of messages that the slave
device has detected in the communications
system since its last restart, clear counters
operation, or power-up.
The number of CRC or LRC errors encountered
by the slave device since its last restart, clear
counters operation, or power-up.
The number of Modbus exception responses
sent by the slave device since its last restart,
clear counters operation, or power-up.
The number of messages addressed to the
slave device or broadcast that the slave device
has processed since its last restart, clear
counters operation, or power-up.
The number of messages addressed to the
slave device for which it sent no response
(neither a normal response nor an exception
response) since its last restart, clear counters
operation, or power-up.
The number of messages addressed to the
slave device that it could not handle due to a
character overrun condition since its last
restart, clear counters operation, or power-up .
The function code received in the query is not an
allowable action for the slave device
2.2).
The data address or number of items received in
the query is not allowable or correct for the slave
device. The slave device will send this exception
response if an attempt to read or write part of a
multiple register database object is detected.
Possible objects are time, strings and counters
(see paragraph
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