PIC24FJ128GA310 datasheet(168/406 Pages) MICROCHIP

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PIC24FJ128GA310 FAMILY

DS39996F-page 168

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11.1.1

I/O PORT WRITE/READ TIMING

One instruction cycle is required between a port direction

change or port write operation and a read operation of

the same port. Typically, this instruction would be a NOP.

11.1.2

OPEN-DRAIN CONFIGURATION

In addition to the PORT, LAT and TRIS registers for data

control, each port pin can also be individually configured

for either a digital or open-drain output. This is controlled

by the Open-Drain Control register, ODCx, associated

with each port. Setting any of the bits configures the

corresponding pin to act as an open-drain output.

The open-drain feature allows the generation of

outputs higher than VDD (e.g., 5V) on any desired

digital only pins by using external pull-up resistors. The

maximum open-drain voltage allowed is the same as

the maximum VIH specification.

11.2

Configuring Analog Port Pins

(ANSx)

The ANSx and TRISx registers control the operation of

the pins with analog function. Each port pin with analog

function is associated with one of the ANS bits (see

the pin function should be analog or digital. Refer to

Table 11-1 for detailed behavior of the pin for different

ANSx and TRISx bit settings.

When reading the PORT register, all pins configured as

analog input channels will read as cleared (a low level).

11.2.1

ANALOG INPUT PINS AND

VOLTAGE CONSIDERATIONS

The voltage tolerance of pins used as device inputs is

dependent on the pin’s input function. Most input pins are

able to handle DC voltages of up to 5.5V, a level typical

for digital logic circuits. However, several pins can only

tolerate voltages up to VDD. Voltage excursions beyond

VDD on these pins should always be avoided.

Table 11-2 summarizes the different voltage tolerances.

Refer to Section 32.0 “Electrical Characteristics” for

more details.

TABLE 11-1:

CONFIGURING ANALOG/DIGITAL FUNCTION OF AN I/O PIN

Pin Function

ANSx Setting

TRISx Setting

Comments

Analog Input

It is recommended to keep ANSx = 1.

Analog Output

It is recommended to keep ANSx = 1.

Digital Input

Firmware must wait at least one instruction cycle

after configuring a pin as a digital input before a valid

input value can be read.

Digital Output

Make sure to disable the analog output function on

the pin if any is present.

TABLE 11-2:

INPUT VOLTAGE LEVELS FOR PORT OR PIN TOLERATED DESCRIPTION INPUT

Port or Pin

Tolerated Input

Description

PORTA<15:14, 7:0>(1)

5.5V

Tolerates input levels above VDD; useful

for most standard logic.

PORTB<15:7, 5:2>

PORTC<3:1>(1)

PORTD<15:8, 5:0>(1)

PORTE<9:8, 4:0>(1)

PORTF<13:12, 8:0>(1)

PORTG<15:12, 9, 6:0>(1)

PORTA<10:9>(1)

VDD

Only VDD input levels are tolerated.

PORTB<6, 1:0>

PORTC<15:12, 4>(1)

PORTD<7:6>

PORTE<7:5>(1)

PORTG<8:7>

Note 1:

Not all of these pins are implemented in 64-pin or 80-pin devices. Refer to Section 1.0 “Device Overview”

for a complete description of port pin implementation.

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