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8.3.7 Codes Supported
Function 3 (03 hex) Read holding registers. (4X)
Function 4 (04 hex) Read input registers. (3X)
Function 16 (10 hex Preset Multiple register. (4X)
Function 17 (11 hex) Report slave ID
BROADCAST is not supported and this command does not
cause the slave to respond to the master.
An EXCEPTION error will be generated if the node cannot
fulfil the task set by the Master or the Slave receives invalid
data in its data slot.
Exception code table
Code
Name
01
Illegal Function
02
Illegal Data Address
03
Illegal Data Value
8.3.8 Modbus Codes Reference
Function 4 (04 hex) - read input registers. (3X)
These registers contain the measured and calculated values
of the instrument. Register addresses in the instrument start
at 0 but in keeping with Modicon Modbus codes, are
designated addresses starting at 40001.
Packet from master format :
[Node Addr][04][reg start addr(2 bytes)][No. of reg (2
bytes)] [CRC(2 bytes)]
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