ThingMagic M5e-Compact - Manual (Page 56)

Reader-to-Host Communication
56 Overview of the Communication Protocol
CCITT CRC-16 Calculation
The same CRC calculation is performed on all serial communications between the host
and the reader. The CRC is calculated on the Data Length, Command, Status Word, and
Data bytes. The header (SOH, 0xFF) is not included in the CRC.
A sample implementation of the CCITT CRC-16 algorithm is shown in this section. The
CRC_calcCrc8()
function is written to calculate the CRC one byte at a time, with the
calculated value stored in crc_calc. The crc_calc value must be pre-loaded the first time
the CRC_calcCrc8() function is called with 0xFFFF to initialize the calculated CRC. The
final value of crc_calc is sent as the 16-bit CRC at the end of the message.
1.The minimum packet length is 7 bytes and the maximum packet length is 255 bytes.
2.Each host command receives a response from the reader. In the response packet, the Header, Data Length, Command, Data, and
Checksum are functionally similar to the command packet.
3.The only difference is the addition of the Status Word field. The Status Word has two types of values. A Status Word value of 0
(Zero) means the command received was successful. Any other value represents a fault.