ST10F269Z2T3 datasheet(105/184 Pages) STMICROELECTRONICS

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ST10F269

16 - REAL TIME CLOCK

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16 - REAL TIME CLOCK

The Real Time Clock is an independent timer,

which clock is directly derived from the clock

oscillator on XTAL1 input so that it can keep on

running even in Idle or Power down mode (if

enabled to). Registers access is implemented

onto the XBUS. This module is designed for the

following purposes:

– Generate the current time and date for the system

– Cyclic time based interrupt, provides Port

2 external interrupts every second and every

n seconds (n is programmable) if enabled.

– 58-bit timer for long term measurement

– Capable to exit the ST10 chip from power down

mode (if PWDCFG of SYSCON set) after a pro-

grammed delay.

The real time clock is base on two main blocks of

counters. The first block is a prescaler which

generates a basic reference clock (for example a

1 second period). This basic reference clock is

coming out of a 20-bit DIVIDER (4-bit MSB

RTCDH counter and 16-bit LSB RTCDL counter).

This 20-bit counter is driven by an input clock

derived from the on-chip high frequency CPU

clock, predivided by a 1/64 fixed counter (see

Figure 51). This 20-bit counter is loaded at each

basic reference clock period with the value of the

20-bit PRESCALER register (4-bit MSB RTCPH

value of the 20-bit RTCP register determines the

period of the basic reference clock.

A timed interrupt request (RTCSI) may be sent on

each basic reference clock period. The second

block of the RTC is a 32-bit counter (16-bit RTCH

and 16-bit RTCL). This counter may be initialized

with the current system time. RTCH/RTCL counter

is driven with the basic reference clock signal. In

order to provide an alarm function the contents of

RTCH/RTCL counter is compared with a 32-bit

alarm register (16-bit RTCAH register and 16-bit

RTCAL register). The alarm register may be

loaded with a reference date. An alarm interrupt

request (RTCAI), may be generated when the

value

RTCH/RTCL

counter

matches

the

reference date of RTCAH/RTCAL register.

The timed RTCSI and the alarm RTCAI interrupt

requests can trigger a fast external interrupt via

EXISEL register of port 2 and wake-up the ST10

chip when running power down mode. Using the

RTCOFF bit of RTCCON register, the user may

switch off the clock oscillator when entering the

power down mode.

Figure 50 : ESFRs and Port Pins Associated with the RTC

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EXISEL

EXISEL External Interrupt Source Selection register (Port 2)

1 second timed interrupt request (RTCSI) triggers firq[2] and alarm interrupt request (RTCAI) triggers firq[3]

RTC data and control registers are implemented onto the XBUS.

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CCxIC

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