For analog output / value objects, MODBUS Master is expected to send one of the
following MODBUS write requests, all three options are accepted:
●
WriteMultipleReg.req (FC=16, StartAddr, QuantityOfReg=4, ByteCount=8,
data=(2 Registers with 32bit real value; 1 Register with Cmd and Priority field;
1 Register with void value))
●
WriteMultipleReg.req (FC=16, StartAddr, QuantityOfReg=3, ByteCount=6,
data=(2 Registers with 32bit real value; 1 Register with Cmd and Priority field))
●
WriteMultipleReg.req (FC=16, StartAddr, QuantityOfReg=2, ByteCount=4,
data=(2 Registers with 32bit real value)).
In this case, Default-Priority 13 is used
Example of a binary/multistate input object (extended read):
Input register address
Data item structure
X
Present value
X+1
Status flags
Voidfield(=0:0)
X+2
Reliability
Example of a binary/mutistate output object (extended read/write):
Holding register address
Data item structure
X
Present value
X+1
Status Flags
Cmd(=Ready)
Priority
X+2
Reliability
Register
Address
b15 b14 b13 b12 b11 b10 b9
b8
b7
b6
b5
b4
b3
b2
b1
b0
x
Present value
x+1
r(0)
r(0)
r(0)
r(0)
Status flags
Cmd
Priority
x+2
Reliability
Data item structure for 16bit data and Mapping=Extended
For binary and multistate output and value objects, the MODBUS Master is
expected to send one of the following MODBUS write requests, all four options are
accepted:
●
WriteMultipleReg.req (FC=16, StartAddr, QuantityOfReg=3, ByteCount=6,
data=(1 Register with 16bit multistate value; 1 Register with Cmd and Priority
field; 1 Register with void value))
●
WriteMultipleReg.req (FC=16, StartAddr, QuantityOfReg=2, ByteCount=4,
data=(1 Register with 16bit multistate value; 1 Register with Cmd and Priority
field))
●
WriteMultipleReg.req (FC=16, StartAddr, QuantityOfReg=1, ByteCount=2,
data=(1 Register with 16bit multistate value)).
In this case, Default-Priority 13 is used.
●
WriteSingleReg.req (FC=06, StartAddr, 16bit multistate value).
In this case, Default-Priority 13 is used.
Engineering of communicative devices
Modbus slave
6
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A6V10733786_en_c
