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MVI56-MCM
♦
ControlLogix Platform
Reference
Modbus Communication Module
Page 130 of 159
ProSoft Technology, Inc.
July 24, 2008
The example below requests the contents of register 3009 in slave number 11.
Adr Func Data Start Reg Hi Data Start Reg Lo Data #of Regs Hi
Data #of Regs Lo
Error Check
Field
11
04
00 08 00 01 CRC
Response
The addressed slave responds with its address and the function code followed by
the information field. The information field contains 1 byte describing the quantity
of data bytes to be returned. The contents of the registers requested (DATA) are
2 bytes each, with the binary content right justified within each pair of characters.
The first byte includes the high order bits and the second, the low order bits.
Because the slave interface is normally serviced at the end of the controller's
scan, the data will reflect the register content at the end of the scan. Each PC will
limit the quantity of register contents provided each scan; thus for large register
quantities, multiple PC scans will be required, and the data provided will be form
sequential scans.
In the example below the register 3009 contains the decimal value 0.
Adr
Func
Byte Count
Data Input Reg Hi
Data Input Reg Lo
Error Check Field
11 04 02
00
00
E9
8.9.5 Force Single Coil (Function Code 05)
Query
This message forces a single coil either ON or OFF. Any coil that exists within
the controller can be forced to either state (ON or OFF). However, because the
controller is actively scanning, unless the coil is disabled, the controller can also
alter the state of the coil. Coils are numbered from zero (coil 0001 = zero, coil
0002 = one, etc.). The data value 65,280 (FF00 HEX) will set the coil ON and the
value zero will turn it OFF; all other values are illegal and will not affect that coil.
The use of slave address 00 (Broadcast Mode) will force all attached slaves to
modify the desired coil.
Note: Functions 5, 6, 15, and 16 are the only messages that will be recognized as valid for
broadcast.
The example below is a request to slave number 11 to turn ON coil 0173.
Adr
Func
Data Coil # Hi
Data Coil # Lo
Data On/off Ind
Data
Error Check Field
11 05 00
AC
FF
00
CRC
Response
The normal response to the Command Request is to re-transmit the message as
received after the coil state has be altered.
Adr
Func
Data Coil # Hi
Data Coil # Lo
Data On/ Off
Data
Error Check Field
11 05 00
AC
FF
00
CRC