The sleep timer is an ultralow-power timer that counts 32-kHz crystal oscillator or 32-kHz RC oscillator periods.The sleep timer runs continuously in all operating modes except power mode 3 (PM3). Typical applications ofthis timer are as a real-time counter or as a wake-up timer to come out of power mode 1 (PM1) or 2 (PM2).The battery monitor comparator enables simple voltage monitoring in the devices that do not include an ADC. Itis designed such that it is accurate in the voltage areas around 2 V, with lower resolution at higher voltages.The random-number generator uses a 16-bit LFSR to generate pseudorandom numbers, which can be read bythe CPU or used directly by the command strobe processor. It can be seeded with random data from noise in theradio ADC.The AES encryption/decryption core allows the user to encrypt and decrypt data using the AES algorithm with128-bit keys. The core is able to support the security operations required by IEEE 802.15.4 MAC security, theZigBee network layer, and the application layer.A built-in watchdog timer allows the CC2533 to reset itself in case the firmware hangs. When enabled bysoftware, the watchdog timer must be cleared periodically; otherwise, it resets the device when it times out. It canalternatively be configured for use as a general 32-kHz timer.USART 0 and USART 1 are each configurable as either a SPI master/slave or a UART. They provide doublebuffering on both RX and TX, as well as hardware flow control, and are thus well suited to high-throughputfull-duplex applications. Each has its own high-precision baud-rate generator, thus leaving the ordinary timersfree for other use |