In the office I hear these terms thrown around as if they are the same. My understanding is that USARTs can deliver the clock signal along with the data.
Are there any other differences? What are the advantages and disadvantages of each?
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UART = Universal Asynchronous Receiver Transmitter
USART = Universal Synchronous Asynchronous Receiver Transmitter
A USART can act in Asynchronous mode just like a UART. But is has the added capability of acting Synchronously. This means that the data is clocked. The clock is either recovered from the data itself or sent as an external signal. The data is regular and bits synchronize with the clock signal. No start and stop bits are used. This allows for a higher baud rate when operating synchronously because bit timings have a certain guarantee and more bits can be used for data instead of as headers.
Whereas a UART has an internal clock signal and data on the bus can have somewhat sloppier and aregular timing. UARTs require start and stop bits and Asynchronous data is only synchronized with the start and stop bits.
That's it, synchronous communication is clocked, while asynchronous is self-timed. The asynchronous UART's main disadvantages:
Synchronous communication doesn't have these disadvantages, and doesn't need a fixed clock frequency. I2C for instance, allows a slave to slow down the clock if it's too fast, by stretching the master's clock pulse. Main disadvantages:
UART requires only data signal.
In UART, the data does not have to be transmitted at a fixed rate.
In UART, data is normally transmitted one byte at a time.
In UART, data transfer speed is set around specific values like 4800, 9600, 38400 bps ,etc.
UART speed is limited around 115200 bps.
In USART, Synchronous mode requires both data and a clock.
In USART’s synchronous mode, the data is transmitted at a fixed rate.
In USART, Synchronous data is normally transmitted in the form of blocks
Synchronous mode allows for a higher DTR (data transfer rate) than asynchronous mode does, if all other factors are held constant..
USART is faster than 115kb.
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