Honeywell HC900 User Manual
Page 39
Modbus/TCP & Modbus RTU Function Codes
Function Code 03- Read Holding (Data) Registers
Revision 10
HC900 Hybrid Controller Communications User Guide
31
12/07
master station requests only one register at an address of a floating point value then half of a float will be
returned.
The Modbus RTU protocol has a single byte count for function code 03, therefore the Modbus RTU
protocol can only process up to 63 floating point and 127 16-bit integer values in a single request.
Example: PV, Remote SP, Working SP, and Output where PV=100.0, RSP=100.0, WSP=100.0, and
Out=55.32 as floating point values where AI #1 = 100.0 and AI #2 = 55.32
Response message format for function codes 03
Slave
Address
(00 for TCP)
Function
Code
Byte
Count
Data Data Data Data
CRC
(RTU)
CRC
(RTU)
TCP Example
00
03
10
42 C8 00 00
(100)
42 C8 00 00
(100)
42 C8 00 00
(100)
42 5D 47 AE
(55.32)
RTU Example
01
03
10
42 C8 00 00
(100)
42 C8 00 00
(100)
42 C8 00 00
(100)
42 5D 47 AE
(55.32)
CRC
CRC