ST72334J2TASLASHXXX datasheet(45/150 Pages) STMICROELECTRONICS

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I/O PORTS (Cont’d)

11.5.1 Register Description

DATA REGISTER (DR)

Port x Data Register

PxDR with x = A, B, C, D, E or F.

Read/Write

Reset Value: 0000 0000 (00h)

Bit 7:0 = D[7:0] Data register 8 bits.

The DR register has a specific behavior according

to the selected input/output configuration. Writing

the DR register is always taken into account even

if the pin is configured as an input; this allows to al-

ways have the expected level on the pin when tog-

gling to output mode. Reading the DR register re-

turns either the DR register latch content (pin con-

figured as output) or the digital value applied to the

I/O pin (pin configured as input).

DATA DIRECTION REGISTER (DDR)

Port x Data Direction Register

PxDDR with x = A, B, C, D, E or F.

Read/Write

Reset Value: 0000 0000 (00h)

Bit 7:0 = DD[7:0] Data direction register 8 bits.

The DDR register gives the input/output direction

configuration of the pins. Each bits is set and

cleared by software.

0: Input mode

1: Output mode

OPTION REGISTER (OR)

Port x Option Register

PxOR with x = A, B, C, D, E or F.

Read/Write

Reset Value: 0000 0000 (00h)

Bit 7:0 = O[7:0] Option register 8 bits.

For specific I/O pins, this register is not implement-

ed. In this case the DDR register is enough to se-

lect the I/O pin configuration.

The OR register allows to distinguish: in input

mode if the pull-up with interrupt capability or the

basic pull-up configuration is selected, in output

mode if the push-pull or open drain configuration is

selected.

Each bit is set and cleared by software.

Input mode:

0: floating input

1: pull-up input with or without interrupt

Output mode:

0: output open drain (with P-Buffer deactivated)

1: output push-pull

DD7

DD6

DD5

DD4

DD3

DD2

DD1

DD0

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