ThingMagic M5e-Compact - Manual (Page 55)

Reader-to-Host Communication
Overview of the Communication Protocol 55
Reader-to-Host Communication
The following diagram defines the format of the generic Response Packet sent from the
reader to the host. The Response Packet is different in format from the Request Packet.
The fields are summarized in the following table.:
Field Length Description
Header (Hdr) 1 byte Defines the start of the packet. Equal to 0xFF
1
Data Length (Len)
1 byte Defines the length, M , of the data field contained in the
packet. Length can be 0 – 248 bytes
2
Command
1 byte OpCode of the last command received
3
Status Word
2 bytes Specifies the status of the last command, Successful =
0x0000, else it contains a fault code.
Data M bytes
(0 to 248)
Defines the binary data returned by the reader in response to
a command. This could, for example, represent data read
from a transponder. Data length,
M , can be a minimum of 0
and a maximum of 248 bytes.
CRC-16 Checksum
(CRC HI, CRC LO) 2 bytes CRC-16 checksum (high order byte first). CRC polynomial is
CCITT CRC-16, with a preload of 0xFFFF. This does not fully
specify the operation of the CRC, see
CCITT CRC-16 Calcu-
lation .
Header Data Length Command Data CRC-16 Checksum
Hdr Len Cmd CRC HI CRC LO
1 byte 1 byte 1 byte 2 bytes
Status Word
Status Word
0 to M bytes 2 bytes