Raspberry与Arduino USB通信协议确认（基于SerialPy库）

Great question—this is a super common point of confusion when working with serial over USB, especially for academic write-ups where precision matters. Let’s break this down clearly:

• First, untangle UART vs. RS-232

  • UART (Universal Asynchronous Receiver/Transmitter) is the core hardware mechanism that handles asynchronous serial data transfer (using start/stop bits instead of a shared clock). Every Arduino has a UART built into its main microcontroller (e.g., ATmega328P on an Uno). It’s the "engine" of serial communication.
  • RS-232 is an electrical and physical layer standard, not a communication protocol itself. It defines specific voltage levels (e.g., +12V for logic 0, -12V for logic 1) and connector types (like DB9) to implement UART over a physical cable. It’s just one way to wire UART communication.

• What’s actually happening with USB + pySerial?

  • Most Arduino boards don’t have native USB support on their main chip. Instead, they use a USB-to-UART bridge chip (like CH340, FT232, or the ATmega16U2 on Uno) that converts USB signals to UART signals compatible with the Arduino’s microcontroller.
  • When you connect via USB and use pySerial, the library abstracts the USB layer entirely—you’re effectively talking directly to the Arduino’s UART port through the bridge.
  • This setup does not use RS-232: the USB cable uses USB’s own electrical standard, and the bridge chip handles all level conversion between USB and the Arduino’s 5V logic UART. RS-232’s high-voltage levels never come into play here.

• Precise phrasing for your final report

  The communication between Raspberry Pi and Arduino via USB (using the pySerial library) relies on UART as the underlying serial communication mechanism, mediated by a USB-to-UART bridge chip integrated on the Arduino board. RS-232 is not involved in this setup, as the physical layer uses USB’s electrical standard rather than RS-232’s voltage specifications.

• Bonus: Direct GPIO UART connection (no USB)
  If you ever connect Arduino’s TX/RX pins directly to Raspberry Pi’s GPIO UART pins, you’re still using UART—but you’ll need level shifters (Arduino uses 5V logic, Pi uses 3.3V). Even then, it’s not RS-232 unless you add transceivers like the MAX232 to convert logic levels to RS-232 standards.

内容的提问来源于stack exchange，提问作者Mark Truong