Specifications

5.3. TRANSPONDER DATA FORMAT AND PROTOCOL
will be able to determine that at least one penguin was within range. The
antennas and gates thus need to be carefully designed to ensure that only
one penguin is within range at a time.
5.3.1 64 Data Bits
The 64 identification bits are s ubdivided into five fields to identify the type
of tagged item. These data fields are also defined in ISO11784/85 as shown
in Table 5.2 [9]:
Number of Bits Field Allocation
1 Animal or Industrial classification
14 Reserved
1 Additional Data Flag
10 ISO 3166 numeric-3 Country Code
38 National Identification Code
Table 5.2: ISO 11784 64bit Transponder ID data fields.
5.3.2 CRC Verification
In order to verify the integrity of the received data, a CRC check must be
performed for each read. The CRC check employed in TI ’s Series 2000
is CRC-16-CCITT format and the checksum is housed in the two Block
Check Character (BCC) bytes of the received data [1]. The CRC-16-CCITT
polynomial is a popular specification (used in Bluetooth, PPP, IrDA and
many other communication standards) with a 16 bit generator polynomial
of x
16
+ x
12
+ x
5
+ 1 [10]. The CRC checksum generation operation can be
modelled as a serial shift through a 16bit register, multiplied by x
16
, followed
by a division by the generating polynomial. The remainder of this operation
is the CRC checksum [11].
The CRC integrity check is fallible. Table 5.3 shows the probability of an
error occurring and the CRC-16 algorithm detecting the error.
The probability of an error occurring and the CRC check not flagging it
is so small as to be inconsequential for the purposes of this project.
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