Serial Communication Methods

Serial Communication

• Asynchronous serial transmission: sender does not share a clock signal with the receiver, and both agree on timing parameters in advance.
• Synchronous serial transmission: sender and receiver share a common clock signal, ensuring more efficient transmission.

Serial-to-Parallel and Parallel-to-Serial Conversion

• Serial communication involves transmitting data over a single wire, converting parallel data to serial format.
• Clock signal is sent with serial data in synchronous communication systems.

ASCII Encoding

• ASCII (American Standard Code for Information Interchange) encodes 128 characters, including 95 printable characters and 33 non-printing control characters.
• ASCII characters can be represented by 7 bits, commonly stored as one byte for storage convenience.

UTF-8 Encoding

• UTF-8 (UCS Transformation Format—8-bit) is a variable-width encoding scheme derived from ASCII.
• UTF-8 avoids endianness and byte order marks, making it widely used for the World Wide Web.

MBED UART API

• The mbed API provides functions to access the UART peripheral, including:
  • Creating a Serial port with specified transmit and receive pins.
  • Setting the baud rate and transmission format.
  • Determining if a character is available to read or write.
  • Attaching a function to call whenever a serial interrupt is generated.

Simple Example: send periodic message to PC

• Uses the mbed UART API to send a periodic message to the PC via UART.

Mbed UART Sample Program

• Defines two serial connections: pc for printing debug messages and uart for UART communication.
• 示例代码使用putc()和getc()函数来send和receive数据。

UART Example 2

• Communicates with two separate devices having different UART baud rates.
• Uses two Serial objects for UART communication and sets the baud rate accordingly.

Serial Peripheral Interface (SPI) Bus

• SPI is a synchronous communication protocol requiring a clock wire.
• SPI bus has four wires: SCLK, MOSI, MISO, and CS (chip select).
• Devices communicate in master/slave mode, with the master initiating data transfers.

SPI Overview

• SPI bus features:
  • Synchronous communication.
  • Four-wire serial bus.
  • Devices communicate in master/slave mode.
  • Multiple slaves are enabled individually by the select lines.

SPI Master and Slave

• Master: initiates data transfers and asserts the CS line of the target peripheral.
• Slave: responds to the master's data transfer requests.

SPI Port on STM32F411RET6

• The SPI pins on the STM32F411RET6 are:
  • SPI1: MOSI (PA7), MISO (PA6), SCK (PA5), and NSS/CS (PA4).
  • SPI2: MOSI (PB15), MISO (PB14), SCK (PB13), and NSS/CS (PB12).
  • SPI3: MOSI (PC12), MISO (PC11), SCK (PC10), and NSS/CS (PA15 or PA4).

SPI Modes: Clock Polarity and Clock Phase

• SPI provides four communication modes based on Clock Polarity (CPOL) and Clock Phase (CPHA).
• CPOL and CPHA can be specified as '0' or '1' to form four unique modes.

MBED SPI API

• The mbed API provides functions to access the SPI peripheral, including:
  • Creating a SPI master connected to the specified pins.
  • Configuring the data transmission format.
  • Setting the SPI bus clock frequency.
  • Writing data to the SPI slave and returning the response.