Mode 0 has absolute nothing to do with the UART functionality

It converts the UART hardware into a SPI to control shift registers, like 74HC165, 74HC595 or so.

In mode 0 the TX pin was always the shift clock output and RX was the open drain input and output. Thus no baud rate generator was needed and also absolutely no influence of the crystal value occur.

Real UART modes are only mode 1, 2 or 3 !


I used never the mode 0, because often separate pins are needed for input and output and thus 8051 with its own SPI are more useful, e.g. AT89C51ED2.


Peter