During the prebit reception phase, the bits the transponder transmits show the low-bit frequency, which is the resonance frequency of the transponder. The time periods of the prebits are evaluated by the demodulator counter. Based on the counter states, an algorithm is implemented that ensures a correct measurement of the resonance frequency of the transponder:

1. A time period of the low-bit frequency has a counter state between 112 and 125.
2. The measurement of the low-bit frequency (the average of eight subsequent counter states) is accepted during the write mode, when the eight time periods have counter states in the defined range. The measurement during write mode is started with the falling edge at TXCT using the fixed delay time at which end the full bridge is switched on again.
3. The counter state of the measured low-bit frequency results in the average counter state of an accepted measurement and can be used to update the register of the programmable frequency divider.
4. The measurement of the low-bit frequency (the average of eight subsequent counter states) is accepted during the read mode, when the eight time periods have counter states in the defined range. The start of the measurement during read mode is delayed to use a stable input signal for the measurement.
5. The threshold to distinguish between high-bit and low-bit frequency is calculated to be by a value of 5 or 7 (see hysteresis in threshold) higher than the counter state of the measured low-bit frequency.