Manual – Starflow QSD Model 6527B and 6537A
Unidata Manual - 6527B and 6537A Starflow QSD User Manual 08 05 2023.docx
Page 28
5.2.3. Slave Response Format
Device Address
Function Code
Data Payload
CRC
Device Address – Echo of the device address sent in the master message to the device.
Function code – Echo of function code sent in the master message to the device.
Data payload – 0-N bytes with the response from the device.
CRC - 2 bytes with a value computed mathematically.
5.2.4. Standard Message Format
Read Holding Registers
are used to retrieve measurements.
Message
Response
Address 1
byte
1-247
Address 1
byte
1-247
Function Code
1 byte
0x03
Function Code 1 byte
0x03
Data Address
2 bytes
0 to 0xFFFF
Byte Count
1 byte
Register Count
2 bytes
Data Payload
N bytes
CRC 2
bytes
CRC 2
bytes
*Byte count = 2*Register Count
Write Single Register
is used to configure instrument settings.
To set a single register in a device:
Message
Response
Address 1
byte
1-247
Address 1
byte
1-247
Function Code
1 byte
0x06
Function Code 1 byte
0x06
Data Address
2 bytes
0 to 0xFFFF
Byte Count
1 byte
0 to 0xFFFF
Register Count
2 bytes
0 to 0xFFFF
Data Payload
N bytes
0 to 0xFFFF
CRC 2
bytes
CRC 2
bytes
RS485 Settings
Baud rates – Support Baud rates from 9600 to 115200
Data Bits – 8 data bits (7 data bits is not a valid setting for Modbus RTU)
Parity Bits – Even, Odd and None
Stop Bits – 1 or 2
*Default settings will be 9600,8,N,1
.