Functional overview
STM32F042xx
DocID025832 Rev 2
The RTC is an independent BCD timer/counter. Its main features are the following:
Calendar with subseconds, seconds, minutes, hours (12 or 24 format), week day, date,
month, year, in BCD (binary-coded decimal) format.
Automatically correction for 28, 29 (leap year), 30, and 31 day of the month.
Programmable alarm with wake up from Stop and Standby mode capability.
On-the-fly correction from 1 to 32767 RTC clock pulses. This can be used to
synchronize it with a master clock.
Digital calibration circuit with 1
ppm resolution, to compensate for quartz crystal
inaccuracy.
2 anti-tamper detection pins with programmable filter. The MCU can be woken up from
Stop and Standby modes on tamper event detection.
Timestamp feature which can be used to save the calendar content. This function can
triggered by an event on the timestamp pin, or by a tamper event. The MCU can be
woken up from Stop and Standby modes on timestamp event detection.
Reference clock detection: a more precise second source clock (50 or 60 Hz) can be
used to enhance the calendar precision.
The RTC clock sources can be:
A 32.768 kHz external crystal
A resonator or oscillator
The internal low-power RC oscillator (typical frequency of 40 kHz)
The high-speed external clock divided by 32
3.14
Inter-integrated circuit interfaces (I
2
C)
The I
2
C interface (I2C1) can operate in multimaster or slave modes. It can support Standard
mode (up to 100 kbit/s), Fast mode (up to 400 kbit/s) and Fast Mode Plus (up to 1 Mbit/s)
with 20 mA output drive
on some I/Os.
It supports 7-bit and 10-bit addressing modes, multiple 7-bit slave addresses (2 addresses,
1 with configurable mask). It also includes programmable analog and digital noise filters.
In addition, I2C1 provides hardware support for SMBUS 2.0 and PMBUS 1.1: ARP
capability, Host notify protocol, hardware CRC (PEC) generation/verification, timeouts
verifications and ALERT protocol management. I2C1 also has a clock domain independent
Table 8. Comparison of I2C analog and digital filters
Analog filter
Digital filter
Pulse width of
suppressed spikes
50 ns
Programmable length from 1 to 15
I2C peripheral clocks
Benefits
Available in Stop mode
1. Extra filtering capability vs.
standard requirements.
2. Stable length
Drawbacks
Variations depending on
temperature, voltage, process
Wakeup from Stop on address
match is not available when digital
filter is enabled.
