Watlow Series F4P - Manual (Page 95)

Chapter Nine: Communications
Exception Responses . . . . . . . . . . . . . . . . . . . . . . .9.1
Modbus Registers (Alphabetical Order) . . . . . . . . .9.2
Modbus Registers (Numerical Order) . . . . . . . . . . .9.11
Overview
Exception Responses
When a controller cannot process a command it returns an exception response and sets the
high bit (0x80) of the command.
0x01 illegal command
0x02 illegal data address
0x03 illegal data value
Packet returned by controller:| nn | nn | nn | nn nn |
∆ ∆ ∆ ∆ ∆
controller address (one byte)
command + 0x80
exception code (0x01 or 0x02 or 0x03)
CRC low byte
CRC high byte
Wa t l o w S e r i e s F 4 P C o m m u n i c a t i o n s ■ 9 . 1
9
The Series F4P uses Modbus as its communications pro-
tocol. Modbus is a standard protocol developed by A.E.G.
Schneider. Modbus RTU enables a computer or PLC to
read and write directly to registers containing the con-
troller’s parameters. With it you can read all of the con-
troller’s parameters with a few read commands.
If you already have a software application that uses
Modbus, the Modbus Registers Table in this chapter will
provide the register number and values (sometimes
called enumerated types) for each parameter.
Dependencies between parameters do exist. For best re-
sults, program the parameters in the order in which they
appear in the Software Map (inside back cover).
For basic information about writing an application using
Modbus protocol, you may want to download the elec-
tronic F4P Communications Guide from the Watlow web
site: http://www.watlow.com/prodtechinfo. Search on the
key words Data Communications.
✔ NOTE:
For ranges, conditions and other information, look up parameter names in
the Index, which will direct you to earlier chapters in this book.