A sensor chip, code-named Daytona, measures pressure to within 7.5kPa (typical car tyre pressure is 220kPa), and temperature to within 4° Celsius. Temperature measurement is necessary to compensate for pressure changes due to tyre heating during driving.
The Daytona chip is fabricated using low power CMOS technology and draws just 0.55μA on standby. The second chip in the RSM is a combination of Motorola's HC08 microcon-troller and a UHF radio transmitter in a 32-pin package. It processes the raw measurements into a tyre pressure reading and transmits the data to the in-car receiver.
The transmitter operates in the 315, 434 or 868MHz bands, sending the pressure data at up to 9600 baud by either on/off or phase shift keying. The HC08 has 2Kb of on-board FLASH memory and enough I/O and computing power to handle the pressure and temperature reading task.