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STR71X REAL TIME CLOCK APPLICATION EXAMPLE

4 CONFIGURATION MODE

To write in the RTC_PRL, RTC_CNT, RTC_ALR registers, the peripheral must enter Config-

uration mode. This is done by setting the CNF bit in the RTC_CRL register.

In addition, writing to any RTC register is only enabled if the previous write operation is fin-

ished.

To enable the software to detect this situation, the RTOFF status bit is provided in the

RTC_CR register to indicate that an update of the registers is in progress. A new value can be

written to the RTC counters only when the RTOFF status bit value is ’1’.

Configuration Procedure:

1. Poll RTOFF, wait until its value goes to ‘1’

2. Set CNF bit to enter configuration mode

2. Write to one or more RTC registers

3 Clear CNF bit to exit configuration mode

The write operation only executes when the CNF bit is cleared and it takes at least two

Clock32 cycles to complete.

5 32-BIT COUNTER TIME CONVERSION

This application note explains how to convert the 32-bit time value into a date and time value

that can be put in the form of MM/DD/YYYY, HH:MM:SS. Many functions provided by the ARM

compiler used to convert from a date and time to seconds are also described.

These functions are modified in order to explore the STR71x RTC to deliver time and date.

5.1 C LIBRARY FUNCTIONS USED

5.1.1 RTC prescaler Initialisation:

Before start-up we must adjust the STR71x RTC prescaler register value in order to have the

RTC counter registers incremented every second, this can be configured by using a prescaler

value of 0x8000 (32768) to slow down the RTC clock from 32768 Hz to 1 Hz.

5.1.2 Origin Date Adjust

Since the date used in this application note is the same used with the UNIX operating system,

the reference date January 1, 1970, often referred to as Unix Epoch, we must

0x3FF36300 to the value obtained from the STR71x RTC Counter register with intent to have

a start date = 01/01/2004.