MVI56-MCM ♦ ControlLogix Platform Reference
Modbus Communication Module
Page 134 of 159 ProSoft Technology, Inc.
July 24, 2008
8.9.8 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, etc.). 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.
Adr Func Hi Add Lo Add Quantity Byte
Cnt
Data Coil Status
20 to 27
Data Coil Status
28 to 29
Error Check
Field
11 0F 00 13 00 0A 02 CD 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.
8.9.9 Preset Multiple Registers (Function Code 16)
Query
Holding registers existing within the controller can have their contents changed
by this message (a maximum of 60 registers). However, because the controller is
actively scanning, it also can alter the content of any holding register at any time.
the values are provided in binary up to the maximum capacity of the controller
(16-bit for the 184/384 and 584); unused high order bits must be set to zero.
When specified registers with contents specified.
Note: Function codes 5, 6, 15, and 16 are the only messages that will be recognized as valid for
broadcast.
Adr Func Hi Add Lo Add Quantity Byte Cnt Hi Data Lo Data Hi Data Lo Data Error Check Field
11 10 00 87 00 02 04 00 0A 01 02 CRC
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