STPM32 datasheet(50/89 Pages) STMICROELECTRONICS

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8.6.3

UART peripheral

The STPM3x provides the UART interface, which allows a communication using two single direction pins only.

The connection to SCS and SYN pins is recommended to ensure proper device start up and reset procedures.

Main features of this interface are:

•

Full-duplex, asynchronous communication

•

Low-level sequential data exchange protocol (1 start, 8 data, 1 stop)

•

NRZ standard format (mark/space)

•

Fractional baud rate generator system (to offer a wide range of baud rates)

•

Several error detection flags

•

Configurable frame length

•

Optional configurable CRC checksum

•

Optional noise immunity algorithm.

TX pin accesses this interface, which transmits data to the microcontroller, and RX pin, which receives data from

the microcontroller. A simple master/slave topology is implemented on the UART interface where the STPM3x

acts as the slave.

Transmission and reception are driven by a common baud rate generator; the clock for each one is generated

only when UART is enabled.

UART transmitting and receiving sections must have the same bit speed, frame length and stop bits.

Chip selection in UART mode requires SCS bit is kept high.

Communication starts when the master sends slave a valid frame (the microcontroller). The format of the frame is

shown below.

Figure 52. UART frame

Start

Bit

Bit 0

Bit 1

Bit 2

Bit 3

Bit 4

Bit 5

Bit 6

Bit 7

Stop

Bit

Start

Bit

Clock

Start

Bit

Start

Bit

Extra

Idle frame

Break frame

As shown in Figure 52, each frame consists of 10 bits. Each bit is sent to a variable rate. All frame data are sent

LSBfirst.

If a BREAK frame is received, a break flag is set and the whole packet reception aborts. The frame receiver can

recognize an IDLE frame, but packet processing is not involved.

UART control register

US_REG1 and US_REG2 registers respectively contain all the configuration parameters of SPI and UART

interfaces of the STPM3x. Table 29 describes UART bits:

Table 29. UART control register US_REG1

Row bit position

Name

Description

Default value

[23:16]

Timeout

Timeout threshold [ms]

STPM32, STPM33, STPM34

Communication protocol

DS10272 - Rev 13

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