ProSoft Technology MVI69E-MBTCP - Manual (Page 115)

MVI69E-MBTCP ♦ CompactLogix Platform Reference
Modbus TCP/IP Enhanced Communication Module User Manual
ProSoft Technology, Inc. Page 115 of 150
May 20, 2015
Because the server interface is normally serviced at the end of the controller's
scan, the data reflect the register content at the end of the scan. Each PC limits
the quantity of register contents provided each scan; thus for large register
quantities, multiple PC scans are required, and the data provided is from
sequential scans.
In the example below the register 30009 contains the decimal value 0.
Node
Address
Function
Code
Byte Count Data Input
Register High
Data Input
Register Low
Error Check
Field
(2 bytes)
0B 04 02 00 00 E9
7.2.8 Force Single Coil (Function Code 05)
Query
This Function Code forces a single coil (Modbus 0x range) 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, and so on). The data value 65,280
(FF00 HEX) sets the coil ON and the value zero turns it OFF; all other values are
illegal and do not affect that coil.
The use of server address 00 (Broadcast Mode) forces all attached servers to
modify the desired coil.
Note: Functions 5, 6, 15, and 16 are the only messages that are recognized as valid for broadcast.
The example below is a request to server number 11 to turn ON coil 0173.
Note: This is the structure of the message being sent out to the Modbus network. The byte values
below are in hexadecimal display.
Node
Address
Function
Code
Data Start Bit
High
Data Start Bit
Low
Number of
Bits High
Number of
Bits Low
Error Check
Field (2 bytes)
0B 05 00 AC FF 00 CRC