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How can I get rid of variation with uPD78083's UART?

Latest Updated:12/01/2011

Question:

With the uPD78083's UART, there is a variation ranging from 0 to several hundred μs from when data is written to transmit shift register TXS to when data transmission actually starts.
How can I get rid of this variation?

Answer:

This variation occurs because the UART's baud rate clock and the CPU clock are asynchronous.
To avoid this, it is necessary to synchronize the baud rate clock with the CPU operation.
One way to reduce variation is to set TXE of ASIM to 0 when not transmitting, and set TXE prior the start of transmission.
Note, however, that this operation is not guaranteed.
Suitable Products
UPD7808x