ProSoft Technology MVI69E-MBTCP - Manual (Page 119)

MVI69E-MBTCP ♦ CompactLogix Platform Reference
Modbus TCP/IP Enhanced Communication Module User Manual
ProSoft Technology, Inc. Page 119 of 150
May 20, 2015
7.2.11 Force Multiple Coils (Function Code 15)
Query
This function forces each coil (Modbus 0x range) in a consecutive block of coils
to a desired ON or OFF state. 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 coils are disabled, the controller can also alter the state of
the coil. Coils are numbered from zero (coil 00001 = zero, coil 00002 = one, and
so on). The desired status of each coil is packed in the data field, one bit for each
coil (1= ON, 0= OFF). The use of server address 0 (Broadcast Mode) forces all
attached servers to modify the desired coils.
Note: Functions 5, 6, 15, and 16 are the only messages (other than Loopback Diagnostic Test) that
are recognized as valid for broadcast.
The following example forces 10 coils starting at address 20 (13 HEX). The two
data fields, CD =1100 and 00 = 0000 000, indicate that coils 27, 26, 23, 22, and
20 are to be forced on.
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
Coil
Address
High
Coil
Address
Low
Number of
Coils High Number of
Coils Low Byte
Count Force
Data High
20 to 27
Force
Data Low
28 to 29
Error Check
Field (2 bytes)
0B 0F 00 13 00 0A 02 CD 01 CRC
Response
The normal response is an echo of the server address, function code, starting
address, and quantity of coils forced.
Node
Address Function
Code
Coil
Address
High
Coil
Address
Low
Number of
Coils High Number of
Coils Low Error Check
Field (2 bytes)
0B 0F 00 13 00 0A CRC
Writing to coils with Modbus function 15 is accomplished regardless of whether
the addressed coils are disabled or not.