I have the following question that the data-sheet does not mention in detail.

MODE 0
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During serial port mode '0' P3.0 is used for data and P3.1 is used for clock. In this mode the transmission is half-duplex. i.e. one direction at a time, and P3.0 changes direction accordingly. I.e. input port for reception and output port for transmission.

Transmit is enabled by writing to SBUF.

Receive is enabled by clearing RI and setting REN.

Now....

1) What happens if transmission is in progress and the user clears REN? Will the 8051 change direction of the P3.0 port to output immediately and start reception or is the write to REN ignored? If it is ignored, will it be ignored for good, or will the 8051 start reception once transmission has completed?

2) Likewise, during reception, what happens if the used clears REN and writes to SBUF? Will P3.0 change direction to input and start reception or is the write to SBUF ignored? If ignored, will the 8051 start transmission once reception has completed, or is it ignored for good?

3) In Serial Port Mode 0, is P3.0 default input or output?


Jesper

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