What the Event Bytes Contain

This type of event byte is stored by the slave when a query message is received. It is stored
before the slave processes the message. This event is defined by bit 7 set to a logic 1. The other
bits will be set to a logic 1 if the corresponding condition is TRUE. The bit layout is:
Slave Modbus Send Event
This type of event byte is stored by the slave when it finishes processing a query message. It is
stored if the slave returned a normal or exception response, or no response. This event is
defined by bit 7 set to a logic 0, with bit 6 set to a 1. The other bits will be set to a logic 1 if the
corresponding condition is TRUE. The bit layout is:
Slave Entered Listen Only Mode
This type of event byte is stored by the slave when it enters the Listen Only Mode. The event is
defined by a contents of 04 hex. The bit layout is:
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Slave Initiated Communication Restart
This type of event byte is stored by the slave when its communications port is restarted. The
slave can be restarted by the Diagnostics function (code 08), with subfunction Restart
Communications Option (code 00 01).
That function also places the slave into a Continue on Error or Stop on Error mode. If the slave
is placed into Continue on Error mode, the event byte is added to the existing event log. If the
slave is placed into Stop on Error mode, the byte is added to the log and the rest of the log is
cleared to zeros. The event is defined by a contents of zero. The bit layout is:

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