User's Manual

RS232-Transponder Reader
(SECS1-Protocol), Release 0.3 Draft Page 36 of 91
2000-09-29
ID: ID000093
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 Blocknumber
Header
6 Lower Blocknumber
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 the 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.
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 and a 5 bit fixed reader number
(bit8-bit12 = 0x01).
Bit13 to Bit14 are reserved for future extensions!