Watlow CLS200, MLS300 and CAS200 - Manual (Page 33)

Chapter 2: Modbus-RTU Protocol
Communications Specification 27
NOTE
The function will override the controller’s memory protect
state and the coil’s disable state. The forced state will
remain valid until the controller’s logic next solves the coil.
The coil will remain forced if it is not programmed in the
controller’s logic.
x06 Preset Single Register
• Presets a value into a single holding register (registers 40001 to
49999). When broadcast, the function presets the same register refer-
ence in all attached slaves.
NOTE
The function will override the controller’s memory protect
state. The preset value will remain valid in the register until
the controller’s logic next solves the register contents. The
register’s value will remain if it is not programmed in the
controller’s logic.
x08 Diagnostics
• This function provides a series of tests for checking the communica-
tion system between the master and slave, or for checking various
internal error conditions within the slave. Broadcast is not sup-
ported.
• The function uses a 2-byte subfunction code field 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 response.
• Most of the diagnostic queries use a 2-byte data field to send diag-
nostic data or controller information to the slave. Some of the diag-
nostics cause data to be returned from the slave in a data field of a
normal response.
Diagnostic Subfunctions
x00 Return Query Data
• 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)
x00 00 Any Echo Query Data
x01 Restart Communications Option
• 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