Watlow PPC-2000 - Manual (Page 305)

PPC-2000 User’s Guide Appendix A: Modbus Protocol
Doc.# 30002-00 Rev 2.3 Watlow Anafaze 277
Diagnostics 08
This function provides a series of tests for checking the
communication system between the master and slave, or for
checking various internal error conditions within the slave.
Broadcast is not supported.
The function uses a two-byte Sub-function code field in the
query to define the type of test to be performed. The slave
echoes both the function code and sub-function code in a
normal response.
Most of the diagnostic queries use a two-byte data field to send
diagnostic data or control information to the slave. Some of the
diagnostics cause data to be returned from the slave in a data
field of a normal response.
Force Multiple Coils 15
Forces each coil (0X reference) in a sequence of coils to either
ON or OFF. When broadcast, the function forces the same coil
references in all attached slaves.
Preset Multiple Registers 16
Presets values into the sequence of holding registers (4X
references). When broadcast, the function presets the same
register references an all attached slaves.
The following sections detail the Diagnostics (08)
subfunctions.
Diagnostics Subfunction -- Return Query Data 00
The data passed in the query data field is to be returned (looped
back) in the response. The entire response message should be
identical to the query.
Subfunction Data Field (Query) Data Field
(Response)
00 00 Any Echo Query Data
Diagnostics Subfunction -- Restart Communications
Option 01
The slave’s peripheral port is to be initialized and restarted,
and all of its communications event counters are to be cleared.
If the port is currently in Listen Only Mode, no response is
returned. This function is the only one that brings the port out
of Listen Only Mode. If the port is not currently in Listen Only
Mode, a normal response is returned. This occurs before the
restart is executed.
Subfunction Data Field (Query) Data Field
(Response)
00 01 00 00 Echo Query Data
00 01 FF 00 Echo Query Data