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com:basic_uart [2024/12/20 23:57] – [Sources] vamsancom:basic_uart [2025/02/11 20:21] (current) – vamsan
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-====== lamaPLC Communication: UART basic ======+====== lamaPLC Communication: UART / USART basic ====== 
 +===== USART ===== 
 +A **USART** (//universal synchronous/asynchronous receiver/transmitter//) is hardware that enables a device to communicate using serial protocols. It can function in a slower asynchronous mode, like a universal asynchronous receiver/transmitter (UART), or in a faster synchronous mode with a clock signal. USARTs are no longer common in consumer PCs but are still used in industrial equipment and embedded systems. 
 + 
 +===== USART vs. UART ===== 
 +A UART device can use asynchronous communication protocols. A USART device can use both asynchronous and synchronous communication protocols. Therefore, a USART can do anything a UART can do and more. Because a USART requires more complex circuitry and more communication lines to fully implement, many devices may only implement a UART to save on cost, complexity or power usage. 
 + 
 +===== Asynchronous and synchronous serial communication ===== 
 +In serial communication, each bit of data is sent one at a time on a transmit wire. This is a serial communications interface. If the sender and the receiver don't agree on how the data is sent, such as the order and length of time of each bit, then the data becomes garbled, and they won't understand each other. Asynchronous and synchronous are two different ways to standardize how serial data is sent. 
 + 
 +===== Asynchronous serial data ===== 
 +In asynchronous mode, only one data line is used to send data from the transmitter to the receiver. There is no shared synchronization signal from the sender to the receiver. So, the receiver has no way to know how fast or slow the data is coming. To circumvent this, both the sender and receiver must be manually configured beforehand to use the same data rate. A common shared baud rate is 9,600 bits per second. 
 + 
 +===== UART =====
 A //universal asynchronous receiver-transmitter// (**UART**) is a peripheral device for asynchronous serial communication in which the data format and transmission speeds are configurable. It sends data bits one by one, from the least significant to the most significant, framed by start and stop bits so that precise timing is handled by the communication channel. The electric signaling levels are handled by a driver circuit external to the UART. Common signal levels are [[com:basic_rs232|RS-232]], [[com:basic_rs422|RS-422]], [[com:basic_rs485|RS-485]], [[com:basic_gps#gps_applications|GPS-moduls]] and raw TTL for short debugging links. Early teletypewriters used current loops. A //universal asynchronous receiver-transmitter// (**UART**) is a peripheral device for asynchronous serial communication in which the data format and transmission speeds are configurable. It sends data bits one by one, from the least significant to the most significant, framed by start and stop bits so that precise timing is handled by the communication channel. The electric signaling levels are handled by a driver circuit external to the UART. Common signal levels are [[com:basic_rs232|RS-232]], [[com:basic_rs422|RS-422]], [[com:basic_rs485|RS-485]], [[com:basic_gps#gps_applications|GPS-moduls]] and raw TTL for short debugging links. Early teletypewriters used current loops.
  
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 {{ :com:uart3.png |UART letter "A" over 8N1}} {{ :com:uart3.png |UART letter "A" over 8N1}}
-==== Start bit ====+=== Start bit ===
 The start bit signals to the receiver that a new character is coming. The start bit signals to the receiver that a new character is coming.
- +=== Data bit ===
-==== Data bit ====+
 The next five to nine bits, depending on the code set employed, represent the character. The next five to nine bits, depending on the code set employed, represent the character.
- +=== Parity bit === 
-==== Parity bit ==== +If a parity bit is used, it would be placed after all of the data bits. \\ 
-If a parity bit is used, it would be placed after all of the data bits. +
 The parity bit is a way for the receiving UART to tell if any data has changed during transmission. The parity bit is a way for the receiving UART to tell if any data has changed during transmission.
- +=== Stop bit ===
-==== Stop bit ====+
 The next one or two bits are always in the mark (logic high, i.e., '1') condition and called the stop bit(s). They signal to the receiver that the character is complete. Since the start bit is logic low (0) and the stop bit is logic high (1) there are always at least two guaranteed signal changes between characters. The next one or two bits are always in the mark (logic high, i.e., '1') condition and called the stop bit(s). They signal to the receiver that the character is complete. Since the start bit is logic low (0) and the stop bit is logic high (1) there are always at least two guaranteed signal changes between characters.