STR720 datasheet(343/401 Pages) STMICROELECTRONICS

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STR720 - GENERAL PURPOSE I/O PORTS

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23 GENERAL PURPOSE I/O PORTS

23.1 Introduction

The General Purpose IO Port are programmable by software in several conditions: input,

output, Alternate Function, open drain, push-pull, weak push-pull and high impedance. Each

Port is configured in Input (PC0=0, PC1=1, PC2=0, see Table 72 on page 344) during the

Reset phase.

Warning: being each GPIO pin configured in Input during Reset phase, the IO pins are

released to High Impedance condition. To avoid power consumption the user has to drive the

IOs to stable levels.

23.2 Main Features

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Data Input /Output

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Alternate Function

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CMOS Input

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PUSH-PULL Output

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Open Drain Output

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Weak PUSH-PULL Output

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Full software programmability

23.3 Functional Description

The General Purpose IO Port has three configuration registers (PC0,PC1,PC2) and one IO

Data register (PD).

All the allowed Port configurations, set by programming of the configuration registers are

summarized in Table 72 on page 344, where the index (n) is a generic IO bit.

A writing access to the IO Data register always loads the data in the Output Latch.The Output

Latch holds the data to be sent out while the Input Latch captures the data present on the IO

pin.

A reading access to the IO Data register can read the Input Latch or the Output Latch

according to the Port configuration (see later).

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