Watlow CPC400 - Manual (Page 205)

CPC400 Series User’s Guide Appendix A: Modbus Protocol
Doc. 0600-2900-2000 Watlow Anafaze 191
Force Single Coil 05
Forces a single coil (0X reference) to either on or off. When
broadcast, the function forces the same coil reference in all
attached slaves.
Preset Single Register 06
Presets a value into a single holding register (4X refer-
ence). When broadcast, the function presets the same reg-
ister reference in all attached slaves.
Diagnostics 08
Provides a series of tests for checking the communication
system between the master and slave, or for checking var-
ious internal error conditions within the slave. Broadcast is
not supported.
The function uses a two-byte subfunction code in the query
to define the type of test to be performed. The slave echoes
both the function code and subfunction code in a normal re-
sponse.
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.
Table A.2 on page 191 describes the diagnostics (08) sub-
functions.
Table A.2 Diagnostics Subfunctions
Sub-
function
Data Field
Description
Query Response
00 00 Any
Echo Query
Data
Return Query Data (00): Returns (loops back) the data
passed in the query data field. The entire response message
should be identical to the query.
00 01
00 00
Echo Query
Data Restart Communications (01): Initializes and restarts the
slave’s peripheral port, and clears all of its communications
event counters. 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.
FF 00
Echo Query
Data
00 02 00 00
Diagnostic
Register
Contents
Return Diagnostic Register (02): Returns the contents of the
slave’s 16-bit diagnostic register.