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Sheet目录3875

66页 67页 68页 69页 [70页]71页 72页 73页 74页

2007 Microchip Technology Inc.

Preliminary

DS70165E-page 159

dsPIC33F

10.0

I/O PORTS

All of the device pins (except VDD, VSS, MCLR and

OSC1/CLKIN) are shared between the peripherals and

the parallel I/O ports. All I/O input ports feature Schmitt

Trigger inputs for improved noise immunity.

10.1

Parallel I/O (PIO) Ports

A parallel I/O port that shares a pin with a peripheral is,

in general, subservient to the peripheral. The periph-

eral’s output buffer data and control signals are

provided to a pair of multiplexers. The multiplexers

select whether the peripheral or the associated port

has ownership of the output data and control signals of

the I/O pin. The logic also prevents “loop through”, in

which a port’s digital output can drive the input of a

peripheral that shares the same pin. Figure 10-1 shows

how ports are shared with other peripherals and the

associated I/O pin to which they are connected.

When a peripheral is enabled and actively driving an

associated pin, the use of the pin as a general purpose

output pin is disabled. The I/O pin may be read, but the

output driver for the parallel port bit will be disabled. If

a peripheral is enabled, but the peripheral is not

actively driving a pin, that pin may be driven by a port.

All port pins have three registers directly associated

with their operation as digital I/O. The data direction

or an output. If the data direction bit is a ‘1’, then the pin

is an input. All port pins are defined as inputs after a

Reset. Reads from the latch (LATx), read the latch.

Writes to the latch, write the latch. Reads from the port

(PORTx), read the port pins, while writes to the port

pins, write the latch.

Any bit and its associated data and control registers

that are not valid for a particular device will be

disabled. That means the corresponding LATx and

TRISx registers and the port pins will read as zeros.

When a pin is shared with another peripheral or func-

tion that is defined as an input only, it is nevertheless

regarded as a dedicated port because there is no

other competing source of outputs. An example is the

INT4 pin.

FIGURE 10-1:

BLOCK DIAGRAM OF A TYPICAL SHARED PORT STRUCTURE

Note:

This data sheet summarizes the features

of this group of dsPIC33F devices. It is not

intended to be a comprehensive reference

source. To complement the information in

this data sheet, refer to the “dsPIC30F

Family Reference Manual” (DS70046).

Note:

The voltage on a digital input pin can be

between -0.3V to 5.6V.

WR LAT +

TRIS Latch

I/O Pin

WR PORT

Data Bus

Data Latch

Read Port

Read TRIS

WR TRIS

Peripheral Output Data

Output Enable

Peripheral Input Data

I/O

Peripheral Module

Peripheral Output Enable

PIO Module

Output Multiplexers

Output Data

Input Data

Peripheral Module Enable

Read LAT

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