User's Manual

5 OPERATION
34
HF80 Transponder Reader – HSMS, Release 1.3
5.4.2.3 Message Block Structure
SECS message blocks have the form:
Byte msb Description
Length
0 Length without checksum , 10 – 254
1 R Upper Device ID (Reader ID)
2 Lower Device ID (Gateway ID)
3 W Upper Message ID (Stream)
4 Lower Message ID (Function)
5 E Upper Block number
Header
6 Lower Block number
7 System Byte 1
8 System Byte 2
9 System Byte 3
System
Bytes
10 System Byte 4
Text
11 – 254 message text, user data
Checksum
255, 256 16 Bit unsigned checksum
The operation of all communication functions above the block transfer
protocol is linked in information contained in a 10-byte data element,
called the header.
The header is always the first 10 bytes of every block sent by the
block transfer protocol.
The length includes all bytes sent after the length byte, excluding the
two checksum bytes. The maximum block length allowed by SECS-1 is
254 bytes and the minimum is 10 bytes (header only).
The reverse bit (R-bit) signifies the direction of a message. The R-bit
(msb) is set to 0 for messages to the equipment, and set to 1 for
messages to the host.
The device ID is a definite number to contact the reader.
The device ID consists of the 8 bit gateway ID (bit0-bit7), which is
identical with the last two characters of the readers serial number
(default), and a 5 bit fixed reader number (bit8-bit14 = 0x01).
Of course, the ID can be changed within the valid scope.