Datasheet

Functional overview STM32F051x4 STM32F051x6 STM32F051x8
24/121 DocID022265 Rev 6
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
3.16 Inter-integrated circuit interface (I
2
C)
Up to two I
2
C interfaces (I2C1 and I2C2) can operate in multimaster or slave modes. Both
can support Standard mode (up to 100 kbit/s) and Fast mode (up to 400 kbit/s) and, I2C1
also supports Fast Mode Plus (up to 1 Mbit/s) with 20 mA output drive.
Both support 7-bit and 10-bit addressing modes, multiple 7-bit slave addresses (two
a
ddresses, one with configurable mask). They also include 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
from the CPU clock, allowing the I2C1 to wake up the MCU from Stop mode on address
match.
The I2C peripherals can be served by the DMA controller.
Refer to Table 9 for the differences betw
een I2C1 and I2C2.
Table 8. Comparison of I
2
C analog and digital filters
Aspect Analog filter Digital filter
Pulse width of
suppressed spikes
≥ 50 ns
Programmable length from 1 to 15
I2Cx peripheral clocks
Benefits Available in Stop mode
–Extra filtering capability vs.
standard requirements
–Stable length
Drawbacks
Variations depending on
temperature, voltage, process
Wakeup from Stop on address
match is not available when digital
filter is enabled.
Table 9. STM32F051xx I
2
C implementation
I2C features
(1)
I2C1 I2C2
7-bit addressing mode X X
10-bit addressing mode X X
Standard mode (up to 100 kbit/s) X X
Fast mode (up to 400 kbit/s) X X
Fast Mode Plus (up to 1 Mbit/s) with 20 mA output drive I/Os X -
Independent clock X -
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