23 mm Transponder Reference Manual
25 July 1996
Page 6 of 22
The typical data low bit frequency is 134.2 kHz, the typical data high bit frequency is 123.2 kHz.
The low and high bits have different durations, because each bit takes 16 RF cycles to transmit.
The high bit has a typical duration of 130
µ
s, the low bit of 119
µ
s. Figure 5 shows the FM
principle used. Regardless of the number of low and high bits, the transponder response duration
is always less than 20 ms.
The data format consists of 128 bits. Different start/stop bytes and end bits are used, to allow
secure distinction between RO and R/W Transponder. Figures 6a and 6b show the format of the
received data for RO and R/W transponders.
After transmission of the data format the capacitor is discharged. The typical transponder readout
timing is described in figure 4. The charge phase is followed directly by the read phase (RO
mode).
Data encoding is done in NRZ mode (Non Return to Zero). The clock is derived from the RF
carrier by a divide-by-16 function.
Figure 4: Charge and Read Function of the Transponder, Showing the Voltage at the
Transponder and Exciter (Reader) Coil
