ProSoft Technology MVI69L-MBS - Manual (Page 115)

MVI69L-MBS ♦ CompactLogix Platform Reference
Communication Module User Manual
ProSoft Technology, Inc. Page 115 of 154
January 6, 2014
7.2.9 Force Multiple Coils (Function Code 15)
Query
This Function Code 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 Slave address 0 (Broadcast Mode) forces all
attached Slaves 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.
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 Slave 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
The writing of coils via Modbus function 15 is accomplished regardless of
whether the addressed coils are disabled or not.
Coils that are not programmed in the controller logic program are not
automatically cleared upon power up. Thus, if such a coil is set ON by function
code 15 and (even months later) an output is connected to that coil, the output is
hot.