RFID packet format
EM4100 data structure
| 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 9 bit header bits, all 1's |
| 8 bit version number | D00 | D01 | D02 | D03 | P0 | ||||
| or customer ID. | D04 | D05 | D06 | D07 | P1 | ||||
| D08 | D09 | D10 | D11 | P2 | Each group of 4 bits | ||||
| D12 | D13 | D14 | D15 | P3 | is followed by an Even | ||||
| 32 Data Bits | D16 | D17 | D18 | D19 | P4 | parity bit | |||
| D20 | D21 | D22 | D23 | P5 | |||||
| D24 | D25 | D26 | D27 | P6 | |||||
| D28 | D29 | D30 | D31 | P7 | |||||
| D32 | D33 | D34 | D35 | P8 | |||||
| D36 | D37 | D38 | D39 | P9 | |||||
| 4 column Parity bits | PC0 | PC1 | PC2 | PC3 | S0 | 1 stop bit (0) | |||
When the Tag enters the electromagnetic field transmitted by the RFID reader it draws power from the field and will commence transmitting its data as shown above. The first 9 bits are a logic 1. These bits are used as a marker sequence to indicate the beginning of the string. As Even parity is used throughout the data this 9 bit sequence of 1's will not occur at any other location in the string. This is followed by 10 groups of 4 data and 1 even parity bits. Finally there are 4 bits of column parity (Even) and a stop bit (0). The Tag then continues to repeat this string as long as it has power.
Shown here is an example string for a proximity card that has the data 06 (version number),
and 001259E3
as a data string.
| 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 1 | 0 | 1 | 0 | 1 | 0 | 1 | 0 | 1 | 0 | 0 | 1 | 0 | 1 | 1 | 1 | 0 | 1 | 0 | 0 | 1 | 1 | 0 | 0 | 1 | 0 | 0 | 0 |
| 0 | 6 | 0 | 0 | 1 | 2 | 5 | 9 | E | 3 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
FDX-B frequency and modulation
FDX-B protocol based transponders are defined to operate in the 134.2kHz band, and employ a biphase encoding scheme to transmit their information. The data bit rate used is always fc/32.
Biphase encoding schemes modulate the RF field so that there is a transition at the beginning of each bit boundary. A logic 0 state has a transition in the middle of the bit period, while a logic 1 state has no transition during the entire bit period. For FDX-B 1 bit length corresponds to 32 cycles of the activated field of the reader.
| Binary Data | |||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | ||||||||||||||||
| Modulator Control (low means high current) | |||||||||||||||||||||||||||||||
FDX-B data structure
| msb | lsb | ||||||||||
| 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | Header pattern. 11 bits. |
| 1 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | |||
| 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 38 bit (12 digit) National code. | ||
| 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | eg. 000000001008 (decimal). | ||
| 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |||
| 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 10 bit (3 digit) Country code. | ||
| 1 | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 1 | eg. 999 (decimal). | ||
| 1 | - | - | - | - | - | - | - | 1 | 1 bit data block status flag. | ||
| 1 | 1 | - | - | - | - | - | - | - | 1 bit animal application indicator. | ||
| 1 | 1 | 1 | 0 | 1 | 0 | 1 | 1 | 0 | 16 bit checksum. | ||
| 1 | 0 | 1 | 0 | 1 | 1 | 1 | 0 | 1 | |||
| 1 | 0 | 1 | 0 | 1 | 0 | 1 | 1 | 0 | 24 bits of extra data if present. | ||
| 1 | 0 | 0 | 1 | 1 | 0 | 1 | 0 | 0 | eg. $123456. | ||
| 1 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 0 | |||