VRD-485 RFID READER WITH RS-485 INTERFACE
Revision number: 1.01
Review date: 1 December, 2021
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Command 03
‘Read Holding Registers’
This command is used for reading registers in range 0x0000
…
0x000B.
Request:
Request code
1 byte
0x03
Start register
2 bytes
0x0000
… 0x000B
Registers quantity
2 bytes
0x0001
… 0x000B
Response:
Response code
1 byte
0x03
Quantity of following data bytes
1 byte
N x 2
Data (registers values)
N x 2 bytes
N
–
quantity of registers
Example:
REQUEST
RESPONSE
Request code
0x03
Response code
0x03
Start register High number
0x00
Quantity of data bytes
0x04
Start register Low number
0x02
Most significant byte of RFID identifier
value
0xA4
Quantity of High registers
0x00
Next byte of RFID identifier value
0x1E
Quantity of Low registers
0x02
Next byte of RFID identifier value
0x45
Least significant byte of RFID identifier
value
0xC6
In this example there is a request for identifier code, which is stored in 2 registers (total size 4 bytes) at
address 0x0002. If there is no RFID identifier within the area of the reader action
–
then the returned values
will contain zeroes.
Response in case of the request error:
Response code
1 byte
0x83
Error code
1 byte
0x02
–
start register number is more than 0x000B
0x03
–
quantity of requested registers is bigger than memory bounds 0x000B