Force multiple coils (function code 15) – ProSoft Technology MVI69L-MBTCP User Manual

Page 118

Reference

MVI69L-MBTCP ♦ CompactLogix Platform

User Manual

Communication Module

Page 118 of 152

ProSoft Technology, Inc.

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 Server address 0 (Broadcast Mode) will force
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

will be 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)

CRC

Response
The normal response will be 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)

CRC

The writing of coils via Modbus function 15 will be 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
will be hot.