UniData Communication Systems Starflow QSD Manual page 15

4.2.2 Master Format
Device Address
Device address – 1 byte field ranging from 1 to 247. Broadcast address 0
Function code – 1 byte field with a value range 1-127 representing the standard or extended
function code
Data payload – 0-N bytes with response data from the device. Error response will be a 1 byte
value 1-255.
CRC – 2 bytes computed mathematically
4.2.3 Slave Response Format
Device Address
Device Address – Echo of device address sent in master message to the device
Function code – Echo of function code sent in master message to the device
Data payload – 0-N bytes with response from device.
CRC- 2 bytes with a value computed mathematically
4.2.4 Standard Message Format
Read Holding Registers is used to retrieve measurements
Message
Address 1 byte
Function Code 1 byte
Data Address 2 bytes
Register Count 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
Address 1 byte
Function Code 1 byte
Data Address 2 bytes
Register Count 2 bytes
CRC 2 bytes
Unidata Manual - 6527B and 6537A Starflow QSD User Manual 17 01 2020.docx
Manual – Starflow QSD Model 6527B and 6537A
Function Code
Function Code
1-247
0x03
0 to 0xFFFF
1-247
0x06
0 to 0xFFFF
0 to 0xFFFF
Data Payload
Data Payload
Response
Address
Function Code
Byte Count
Data Payload
CRC
Response
Address
Function Code
Byte Count
Data Payload
CRC
CRC
CRC
1 byte 1-247
1 byte 0x03
1 byte
N bytes
2 bytes
1 byte 1-247
1 byte 0x06
1 byte 0 to 0xFFFF
N bytes 0 to 0xFFFF
2 bytes
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