Hardware SerialUART Speed of ATmega328 and ATmega2560 Microcontrollers

Hi

The ATmega328 Microcontroller has 1 SerialUART port, called “serial” in code, on legs 0,1.
The ATmega2560 Microcontroller has 4 SerialUART ports, called “serial” and “serial1”-“serial3” in code, on legs 0,1 and 14-19.

In most Arduino boards that these 2 Microcontrollers are used, there is a USB<->SerialUART chip (e.g. the FTDI FT232RL chip), which is already connected to the first SerialUART port.

But consider a case where you take the ATmega328 and ATmega2560 Microcontrollers,
and put them on a PCB, without a USB<->SerialUART chip.

My question is this:
What is the maximum speed that the ATmega328 and ATmega2560 Microcontrollers’ SerialUART port can get to?

I emphasized the fact that there’s no USB<->SerialUART chip, because this chip is usually a bottleneck compared to the speed that the ATmega chips can give.

So consider the case that you want an ATmega328 or ATmega2560 to communicate with some other module, via SerialUART.

Is there a difference in the maximum speed of the Hardware SerialUART of the ATmega328 and ATmega2560?

Thank you for your help

The relevant Atmega datasheet has tables showing the common baud rates and also a formula for calculating baud rates based on the values in the appropriate registers. I know they can work at 500,000 baud and I thing 1,000,000 baud is possible.

I commonly use 500,000 baud for communication between an Uno or Mega and a PC - but you can certainly also use that speed directly on the Serial pins.

…R
Serial Input Basics - simple reliable ways to receive data.

Thank you Robin

Robin2:
I commonly use 500,000 baud for communication between an Uno or Mega and a PC - but you can certainly also use that speed directly on the Serial pins.

The USB<->SerialUART can get to 500,000baud?
That’s surprising…

card5:
The USB<->SerialUART can get to 500,000baud?
That's surprising..

bdTable.png

bdTable.png

card5:
The USB<->SerialUART can get to 500,000baud?
That’s surprising…

Why?

USB is much faster than that.

…R

USB is much faster than that,
but the USB<->SerialUART is usually not so fast from what I understood from people who tried

card5:
from what I understood from people who tried

I guess they did not try hard enough :slight_smile:

Note that the Arduino Serial Monitor may not be happy working at 500,000baud (I seldom use it so I have not tried).

...R