ST10F269Z2QX Datasheet, PDF (99/161 Pages) STMicroelectronics – 16-BIT MCU WITH MAC UNIT, 256K BYTE FLASH MEMORY AND 12K BYTE RAM

ST10F269Z2Qx
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
register and 16-bit LSB RTCPL register). The
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 of 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
EXISEL
CCxIC
- - - - - - - - YYYY - - - -
- - - - - - - - YYYYYYYY
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.
Figure 51 : RTC Block Diagram
RTCAI RTCSI
Clock Oscillator
RTCCON
AlarmIT
Programmable ALARM Register
RTCAH
RTCAL
Basic Clock IT
Programmable PRESCALER Register
RTCPH RTCPL
=
Reload
RTCH
RTCL
32 bit COUNTER
RTCDH RTCDL
/64
20 bit DIVIDER
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