7733 datasheet(73/940 Pages) RENESAS

73 / 940 page

7733 Group User’s Manual

3–4

PROGRAMMABLE I/O PORTS

3.1.2 Port Pi register

Data is input from or output to an external device by writing/reading data to/from a port register. A port

bit of the port register corresponds to one specified pin. Figure 3.1.3 shows the structure of the port Pi (i

= 0 to 8) register.

(1) How to output data from programmable I/O port

Set the corresponding bit of the port direction register to the output mode.

Write data to the corresponding bit of the port register, and then the data is written into the port

latch.

Data set in the port latch is output.

When a bit of a port register which corresponds to a port set for the output mode is read out, the

contents of the port latch, instead of pin state, is read out. Accordingly, output data can correctly be

read out without influence of external load, etc. (Refer to Figures 3.2.1 and 3.2.2)

(2) How to input data from programmable I/O port

Set the corresponding bit of the port direction register to the input mode.

The pin enters a floating state.

When reading the corresponding bit of the port register in state , data input from the pin can be

read in.

When data is written to a port register which corresponds to a port set for the input mode, the data

is written only into the port latch and not output to the external devices. Pins retain a floating state.

3.1 Programmable I/O ports

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