Specifications

Real-Time Clock (RTC)

11.1 About the Real Time Clock

The PrimeCell Real Time Clock (RTC) PL031 is an Advanced Microcontroller Bus

Architecture (AMBA) compliant System-on-a-Chip (SoC) peripheral that is developed,

tested, and licensed by ARM. The RTC connects to the core APB.

The RTC comprises:

• an AMBA APB interface

• a 32-bit counter

• a 32-bit match register

• a 32-bit comparator.

The CPU reads and writes data, and control and status information through the AMBA

APB interface.

The 32-bit counter is incremented on successive rising edges of the input clock

CLK1HZ. Counting in one second intervals is achieved by using an internal 1Hz clock

signal for CLK1HZ. The counter is free-running. On reset, the counter:

• counts up from one

• reaches the maximum value,

0xFFFFFFFF

• wraps around to zero and continues incrementing.

RTC is loaded or updated by writing to the load register, RTCLR.

Reading the data register, RTCDR, gives the current value of the RTC.

The match register is programmed by writing to RTCMR. The counter and match values

are compared in a comparator. When both values are equal, the interrupt RTCINTR is

asserted HIGH. The CPU can use the interrupt to implement a basic time alarm

function. The interrupt is cleared by writing any data value to the interrupt clear register

RTCICR. The value in the match register can be read at any time.