Note | Basic UART Concept
修網路實作的時候，給學弟妹講解 URAT 跟怎麼在 Arduino 上實作準備的一些教材，簡單介紹下 UART 怎麼在 Arduino 中進行資料傳遞，實驗使用單芯線進行通訊。
How to transfer data between two computers?
- 5 Volts logic:
- Signal on transmission medium
- Metal : Square wave & Sine ware
- Optical fiber : Light square ware
- Wireless : Electromagnetic waves
The Universal Asynchronous Receiver/Transmitter (UART)
UART這種簡單的通訊方式已經存在了幾十年，依然廣受歡迎。
- In a world where technology can become obsolete very quickly
- Still enjoys immense popularity.
Asynchronous communication
UART 是非同步通訊，所代表的是通訊中兩個byte之間的空隙是不固定的，而一個byte中的bit間隔是固定的。因此發送端與接收端都要有相同的 UART 設定。
Capabilities and Characteristics
a basic UART system provides robust, moderate-speed, full-duplex communication with only three signals:
Tx (transmitted serial data), Rx (received serial data), and ground.
一個基本收送的UART傳輸，僅需要三個端口Tx, Rx, GND。但在這之前的前提是 Rx, Tx, 在相同的數據傳輸頻率。
Key Terms
Start bit: The first bit of a one-byte UART transmission. It indicates that the data line is leaving its idle state. The idle state is typically logic high, so the start bit is logic low.- The start bit is an overhead bit; this means that it facilitates communication between receiver and transmitter but does not transfer meaningful data.
Stop bit: The last bit of a one-byte UART transmission. Its logic level is the same as the signal’s idle state, i.e., logic high. This is another overhead bit.
Start bit 代表空閒結束，Srart bit 僅代表開始，不具實際數據。
Stop bit 代表傳輸結束，電位拉高等待下一次 Start。
上圖可以發現發送 10 bit 的資料但其實真正的數據僅有 8 bit。
Baud rate: The approximate rate (in bits per second, or bps) at which data can be transferred.
Example:
9600-baud system，即 1 bit 需要 1/(9600 bps) ≈ 104.2 µs，注意不是實際上每秒傳送 9600 資料，
實際上有開銷 bit 的消耗。
Check bit(Parity bit)
Parity bit: An error-detection bit added to the end of the byte.- Odd or Even
如果要設定校正位，就多傳送一個Bit，並預先設計好 Odd or Even，如今天要傳送 00001110 而 even 即 校正為 1 這樣就會有偶數個 1。
可以看到如果加入 Parity bit，想要發送一個 byte 的成本也增加了 1 個 bit。
Synchronizing and Sampling
the UART interface does not use a clock signal to synchronize the Tx and Rx devices. So how does the receiver know when to sample the transmitter’s data signal?
因為是非同步通訊，所以接收器的 clock 完全獨立於發送器 clock，只需要知道 Start bit 的開始位置後就能依照固定的 clock 進行接收。
Conclusion
所以當今天要設計一個UART單方向傳輸，僅用一條線就可以完成，以預設的頻率收接下來的 8 bit，當電位拉高代表一次傳送的結束，等待下次開始。 這部分可以設計一個 Finite-State Machine 來完成發送與接收的程式設計。
Reference Back to Basics: The Universal Asynchronous Receiver/Transmitter (UART)
Practice One-Line-Communication
Last Edit
11-17-2022 12:07