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Modbus/TCP & Modbus RTU Function Codes
Function Code 05 - Force Single Digital Output
Revision 4 HC900 Hybrid Controller Communications User Guide 29
9/03
4.6 Function Code 05 - Force Single Digital Output
Description
Force a single digital output (0X reference) to either ON or OFF. These are the same digital outputs (DO)
used in Function Code 01.
The Modbus Comm Digital I/O Channel to address mapping is shown in Table 4-5.
The HC900 does not support broadcast, and forcing can only be done in the Run mode.
Query
The query message specifies the DO to be forced. Registers are addressed starting at zero:
DO 1 is bit address 0.
The requested ON/OFF state is specified by a constant in the query data field.
A value of FF 00 hex requests it to be ON.
A value of 00 00 hex requests it to be OFF.
A value of FF FF releases the force.
ATTENTION: Any query (ON or OFF) causes a force mode of this point in the HC900 controller. The
Green force LED goes ON. While in this mode, internal control of function blocks cannot communicate to
this point. DON’T FORGET to send a query to release this force.
Example:
Force DO Card Rack #1, Slot 1, Channel 6 ON in the controller at slave address 1.
Query message format for function code 05
Slave
Address
(00 for TCP)
Function
Code
DO
Address
High
DO
Address
Low
Force
Data
High
Force
Data
Low
CRC
(RTU)
CRC
(RTU)
TCP Example 00 05 00 05 FF 00
RTU Example 01 05 00 05 FF 00 CRC CRC
Response
The normal response is an echo of the query, returned after the DO state has been forced.
Example:
Force DO Card Rack #1, Slot 1, Channel 6 ON in the controller at slave address 1.
Response message format for function code 05
Slave
Address
(00 for TCP)
Function
Code
DO
Address
High
DO
Address
Low
Force
Data
High
Force
Data
Low
CRC
(RTU)
CRC
(RTU)
TCP Example 00 05 00 05 FF 00
RTU Example 01 05 00 05 FF 00 CRC CRC
Table 4-5 shows the Modbus Comm Digital I/O Channel to Address Mapping.