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\nTTL Serial Communication Explained | Part 2\n

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\n\nPublisher:\n\nProgramming Electronics Academy\n\n\n
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\nMany microcontrollers come equipped with a simple way to communicate serially – using a USART. USART stands for Universal Synchronous/Asynchronous Receiver/Transmitter.Wow – that’s one heck of a name! But let’s dive in – it actually way...\nMany microcontrollers come equipped with a simple way to communicate serially – using a USART. USART stands for Universal Synchronous/Asynchronous Receiver/Transmitter.

Wow – that’s one heck of a name! But let’s dive in – it actually way more reasonable than at first glance.

A USART is a piece of hardware. You’ll find it as either a stand-alone integrated circuit, or built right into a microcontroller.

An Arduino UNO for example uses an ATMEGA328P microcontroller which has a built-in USART.

This built-in USART (which uses the RX/TX pins on the Arduino) can send bytes of data serially to a different microcontroller on the Arduino UNO board, the ATMEGA16U2, which is used to handle the serial communication over USB.

USARTs allow us to take data in parallel from one device, convert it into a serial transmission, and then transform it back again into parallel data.

Now I want to draw attention to the Synchronous/Asynchronous part of USART for a moment – because that I think is most confusing. When serial communication protocols are synchronous (for example I2C, SPI) they use a clock signal for synchronizing the transmission from the sender to the receiver. The clock signal is what actively keeps the two in unison.

With an asynchronous protocol, there is no clock signal to synchronize the communication – which is why it requires a baud rate the receiver and the transmitter agree upon beforehand. We’ll be talking more about baud rate in just a moment.

The flavor of serial communication between these two USARTS is often referred to as TTL serial. TTL stands for Transistor-Transistor-Logic (We will not be diving into the details of TTL in this discussion).

It’s this TTL serial communication that we will use as a basis for our discussion of serial communication.

THE NITTY GRITTY OF TTL SERIAL COMMUNICATION
How does it work? Well it’s pretty cool.

Each USART has a TX and RX pin. The TX pin of the sending device is connected to the RX pin of the receiving device and vice versa.

By modulating the TX pin state (Making it HIGH to send a 1, or LOW to send a 0), the sender is able to send a message over a connecting wire. The receiver reads the pin state at its RX pin to determine what was sent.

The serial communication protocol goes something like this…

Send a start bit (0 – LOW) “Hey, I’m getting ready to send a message!”
Followed by a set number of bits (often 8) “Here is my message…”
Optionally a parity bit “You sure you got this right?”
And finally a stop bit (1 – HIGH) “That’s all she wrote”
This is the kind of serial communication that is taking place when using the Arduino serial library, for example with functions like Serial.begin() and serial.print().
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\nProgramming Electronics Academy\n\n
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2021
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arduino, arduino(brand), arduino tutorial, arduino lesson, open source hardware group, learning arduino, microcontrollers, arduino ide, arduino sketch, c++, programming electronics academy, electronics basics, serial communication, serial communication explained, electronics basics for beginners, arduino python, electronics projects, computer programming for beginners, electronics technician, electronics for beginners, electronics repair, ttl serial, receive pin, pin state, data frame, transmit pin, transmit, kind, high, send, message
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