Watlow CLS200, MLS300 and CAS200 User Manual download pdf (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

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

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Watlow CLS200, MLS300 and CAS200 User Manual Page 33