Reference MVI46-MCM
User Manual Modbus Communication Module
5.6.9 Force Multiple Coils (Function Code 15)
Query
This message forces each coil 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) will force 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 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.
Add Lo
Add
Quantity Byte
11 0F 00 13 00
Cnt
Data Coil Status
20 to 27
0A 02
Data Coil Status
28 to 29
CD
Error Check
Field
00 CRC
Response
The normal response will be an echo of the Slave address, function code, starting address, and quantity of coils forced.
Adr Func Hi Addr Lo Addr Quantity Error Check Field
11 0F 00 13 00 0A 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 unprogrammed 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.
Page 92 of 108 ProSoft Technology, Inc.
March 29, 2011
