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Basic Electronics » Serial Comm. vs. Clock frequency

May 31, 2010
by kgb
kgb's Avatar

I see that the MCU supports USART and not UART. if it were to support UART, would it be choosing the clock frequency independent to the baud rate? and would choosing a clock frequency of 20 MHz be a problem?

Thanks

May 31, 2010
by hevans
(NerdKits Staff)

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Hi kgb,

The fact that it is a USART module just means it supports both synchronous and asynchronous operation. Most of the time we operate the UART module in asynchronous mode. If you were to try to communicate over the module in synchronous mode the slave would use the XCK pin as its clock input, and signal would be sampled on the rising of falling edges (more like the way an SPI protocol would work).

avrdude and the bootloader rely on the UART module being in asynchronous mode, so you still can't really up the clock frequency without affecting your programming. What some people choose to do is have the 14.7Mhz crystal for programming, then just swap to the 20Mhz crystal to run the program.

Humberto

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