STPM32 datasheet(74/121 Pages) STMICROELECTRONICS

74 / 121 page

Theory of operation

STPM32, STPM33, STPM34

74/121

DS10272 Rev 8

samples, and applying to them the majority rule. This noise immunity algorithm is

automatically enabled: if “noise detection enable” bit is set, all samples must have the

same value to get a valid bit reception. In this case, when noise is detected within a

frame, a noise detection error is issued and the whole packet is discarded.



CRCPolynomial: default polynomial used is 0x07 (x8+x2+x+1).

CRC, in case of UART, has to be calculated on the reversed byte frame, because of the

internal structure of UART blocks.

For example, if the frame to transmit is 04_03_CD_AB, CRC should be calculated on the

frame:

20_C0_B3_D5 -> CRC = 0x16

The frame to send is: 04_03_CD_AB with the reversed CRC = 68

Note:

For UART peripheral, CRC byte is sent reversed only.



Frame delay: delay (expressed as bit periods) in transmitted frames. The bit period

depends on the baud rate divider selection (see below).



Baud rate: set to 9600 default value, the communication baud rate can be programmed

in this configuration register. Theoretical values for configuration register can be

calculated according to the following formulas, where a main clock frequency is

16 MHz, BR is the desired baud rate and BRDIV is the theoretical value of fractional

divider:

Equation 19

Equation 20

Equation 21

where BRRI are bits [15:4] and BRRF are bits [3:0] of the register.

According to the chosen baud rate divider the bit period is:

Equation 22

Table 31. UART control register US_REG2

Row bit position

Name

Description

Default value

[23:16]

Frame delay TX frame-to-frame delay [bit periods]

[15:0]

Baud rate

Fractional baud rate generation

0x0683

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