ProSoft Technology MVI56E-MCM/MCMXT - Manual (Page 165)

MVI56E-MCM ♦ ControlLogix Platform Reference
Modbus Communication Module User Manual
ProSoft Technology, Inc. Page 165 of 199
June 18, 2014
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 reflects 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 3009 contains the decimal value 0.
Adr Func Byte Count Data Input Reg Hi Data Input Reg Lo Error Check Field
0B 04 02 00 00 E9
6.8.6 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 does not affect that coil.
The use of Slave address 00 (Broadcast Mode) forces all attached Slaves 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 Slave 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.
Adr Func Data Coil # Hi Data Coil # Lo Data On/off Ind Data Error Check Field
0B 05 00 AC FF 00 CRC