STPM32 datasheet(45/89 Pages) STMICROELECTRONICS

45 / 89 page

•

If SCS pin is held low the communication method is SPI

•

If SCS pin is held high the communication interface is UART.

For the communication interface selection the SCS pin must be kept low or high for SPI or UART selection

respectively for at least 125ns after the internal clock signal starts.

According to POR sequence in Figure 28, only after the regulated voltages are OK the PWR_OK internal signal

enables the CLKIN signal to the digital section. After two clock periods, the digital section sets and locks the

interface to the selected type. Note that the regulated voltages could be ready later than the Vcc minimum

threshold of 2.5 V, because of the capacitance on VDDA and VDDD pins.

Below a timing diagram of startup and interface selection.

Figure 47. Startup interface selection timing

VCC

Vdda

SCS

3.3 V

2.5 V

Vddd

2.85 V

1.2 V

POW_OK

UART

SPI

t_comm

After the selected communication interface is established, the interface is locked to prevent the communication

method from changes, and SCS pin is used as chip-select for the device.

Pins used by the serial communication peripheral are listed in Table 22.

Table 22. Communication pin description

Name

Function

SPI connection

UART connection

SYN

Synchronization

GPIO , VCC at startup

GPIO, VCC at startup

SCS

Chip-select

-Start-up interface selection at GND

-Chip-select at GND

-Start-up interface selection at VCC

-Chip-select at VCC

SCL

Clock

SPI CLK

Not used

MOSI/RXD

Data in

SPI MOSI

UART RX

MISO/TXD

Data out

SPI MISO

UART TX

8.6

Communication protocol

A single communication session consists of 4 + 1 (optional CRC) bytes full-duplex data sequence organized as

follows:

Table 23. Communication session structures

Byte

Master-side transmitted data

Slave-side transmitted data

ADDRESS for 32-bit register to be read

Previously requested data byte LSB

ADDRESS for 16-bit register to be written

Previously requested data byte 2 out of 4

DATA for 16-bit register to be written, LSB

Previously requested data byte 3 out of 4

DATA for16-bit register to be written, MSB

Previously requested data byte MSB

STPM32, STPM33, STPM34

Communication protocol

DS10272 - Rev 13

page 45/89

STPM32 Datasheet(PDF) 45 Page - STMicroelectronics

STPM32 Datasheet(HTML) 45 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89

Datasheet Download

Link URL