STM32F091XB datasheet(94/127 Pages) STMICROELECTRONICS

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Electrical characteristics

STM32F091xB STM32F091xC

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DocID026284 Rev 3

6.3.22

Communication interfaces

I2C interface characteristics

The I2C interface meets the timings requirements of the I2C-bus specification and user

manual rev. 03 for:

•

Standard-mode (Sm): with a bit rate up to 100 kbit/s

•

Fast-mode (Fm): with a bit rate up to 400 kbit/s

•

Fast-mode Plus (Fm+): with a bit rate up to 1 Mbit/s.

The I2C timings requirements are guaranteed by design when the I2Cx peripheral is

properly configured (refer to Reference manual).

The SDA and SCL I/O requirements are met with the following restrictions: the SDA and

SCL I/O pins are not “true” open-drain. When configured as open-drain, the PMOS

connected between the I/O pin and VDDIOx is disabled, but is still present. Only FTf I/O pins

support Fm+ low level output current maximum requirement. Refer to Section 6.3.14: I/O

port characteristics for the I2C I/Os characteristics.

All I2C SDA and SCL I/Os embed an analog filter. Refer to the table below for the analog

filter characteristics:

Table 65. IWDG min/max timeout period at 40 kHz (LSI)(1)

1. These timings are given for a 40 kHz clock but the microcontroller internal RC frequency can vary from 30

to 60 kHz. Moreover, given an exact RC oscillator frequency, the exact timings still depend on the phasing

of the APB interface clock versus the LSI clock so that there is always a full RC period of uncertainty.

Prescaler divider

PR[2:0] bits

Min timeout RL[11:0]=

0x000

Max timeout RL[11:0]=

0xFFF

Unit

0.1

409.6

0.2

819.2

/16

0.4

1638.4

/32

0.8

3276.8

/64

1.6

6553.6

/128

3.2

13107.2

/256

6 or 7

6.4

26214.4

Table 66. WWDG min/max timeout value at 48 MHz (PCLK)

Prescaler

WDGTB

Min timeout value

Max timeout value

Unit

0.0853

5.4613

0.1706

10.9226

0.3413

21.8453

0.6826

43.6906

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