ProSoft Technology MVI69L-MBS - Manual (Page 111)

MVI69L-MBS ♦ CompactLogix Platform Reference
Communication Module User Manual
ProSoft Technology, Inc. Page 111 of 154
January 6, 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 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 CRC
7.2.6 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 do 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.
Node
Address
Function
Code
Data Start
Point High
Data Start
Point Low
Number of
Points High
Number of
Points Low
Error Check
Field (2 bytes)
0B 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 been altered.