PIC24FJ64GA datasheet(99/262 Pages) MICROCHIP

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Preliminary

DS39881C-page 97

PIC24FJ64GA004 FAMILY

9.0

I/O PORTS

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

OSCI/CLKI) are shared between the peripherals and

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

Trigger inputs for improved noise immunity.

9.1

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 9-1 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 the peripheral is

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 Output Latch register (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 pin 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.

FIGURE 9-1:

BLOCK DIAGRAM OF A TYPICAL SHARED PORT STRUCTURE

Note:

This data sheet summarizes the features

of this group of PIC24F devices. It is not

intended to be a comprehensive reference

source. For more information, refer to the

“PIC24F Family Reference Manual”,

”Section 12. I/O Ports with Peripheral

Pin Select (PPS)” (DS39711).

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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