RLE Protocol Converter V.2.4 - Manual (Page 55)

rletech.com Protocol Converter User Guide 55
Modbus Communications
4.3. RTU Framing
The example below shows a typical Query/Response from an Protocol Converter Wireless
System.
Slave address 2 responds to Function Code 4 with six bytes of hexadecimal data and ends with
CRC16 checksum.
Register Values:
40001 = 0000 (hex)
40002 = 0000 (hex)
40003 = 0001 (hex)
Table 4.2 Read Output Registers Packet Structure
Read Registers Request Packet Read Registers Response Packet
Slave Address (1 byte) Slave Address (1 byte)
03 (Function code) (1 byte) 03 (Function code) (1 byte)
Start Register (2 bytes) Byte count (1 byte)
# of registers to read (2 bytes) First register (2 bytes)
CRC Checksum (2 bytes) Second register (2 bytes)
…
CRC Checksum (2 bytes)
Table 4.3 Output Registers
Register Name Description Units Range
40001 Integer Output Register for Integer data uint16 0-65535
42001 Float Output
* two registers need Register for Float data Uint32 0-65535
Table 4.4 Response Sample
Slave
Address
Function
Code
Count Bytes
of Data
Register
Data
Msb Lsb
Register
Data
Msb Lsb
Register
Data
Msb Lsb
CRC 16
“Lsb”
CRC 16
“Msb”
02 04 06 00 00 00 00 00 01 B5 A3