DSPIC33FJMC202ESS datasheet(123/330 Pages) MICROCHIP

123 / 330 page

DS70283K-page 123

dsPIC33FJ32MC202/204 and dsPIC33FJ16MC304

10.7

I/O Helpful Tips

In some cases, certain pins as defined in TABLE

24-9: “DC Characteristics: I/O Pin Input Speci-

fications” under “Injection Current”, have internal

protection diodes to VDD and VSS. The term

“Injection Current” is also referred to as “Clamp

Current”. On designated pins, with sufficient exter-

nal current limiting precautions by the user, I/O pin

input voltages are allowed to be greater or less

than the data sheet absolute maximum ratings

with nominal VDD with respect to the VSS and VDD

supplies. Note that when the user application for-

ward biases either of the high or low side internal

input clamp diodes, that the resulting current being

injected into the device that is clamped internally

by the VDD and VSS power rails, may affect the

ADC accuracy by four to six counts.

I/O pins that are shared with any analog input pin,

(i.e., ANx), are always analog pins by default after

any reset. Consequently, any pin(s) configured as

an analog input pin, automatically disables the dig-

ital input pin buffer. As such, any attempt to read a

digital input pin will always return a ‘0’ regardless

of the digital logic level on the pin if the analog pin

is configured. To use a pin as a digital I/O pin on a

shared ANx pin, the user application needs to con-

figure the analog pin configuration registers in the

ADC module, (i.e., ADxPCFGL, AD1PCFGH), by

setting the appropriate bit that corresponds to that

I/O port pin to a ‘1’. On devices with more than one

ADC, both analog pin configurations for both ADC

modules must be configured as a digital I/O pin for

that pin to function as a digital I/O pin.

Most I/O pins have multiple functions. Referring to

the device pin diagrams in the data sheet, the pri-

orities of the functions allocated to any pins are

indicated by reading the pin name from

left-to-right. The left most function name takes pre-

cedence over any function to its right in the naming

convention. For example: AN16/T2CK/T7CK/RC1.

This indicates that AN16 is the highest priority in

this example and will supersede all other functions

to its right in the list. Those other functions to its

right, even if enabled, would not work as long as

any other function to its left was enabled. This rule

applies to all of the functions listed for a given pin.

Each CN pin has a configurable internal weak

pull-up resistor. The pull-ups act as a current

source connected to the pin, and eliminates the

need for external resistors in certain applica-

tions. The internal pull-up is to ~(VDD-0.8) not

VDD. This is still above the minimum VIH of

CMOS and TTL devices.

When driving LEDs directly, the I/O pin can source

or sink more current than what is specified in the

VOH/IOH and VOL/IOL DC characteristic specifica-

tion. The respective IOH and IOL current rating only

applies to maintaining the corresponding output at

or above the VOH and at or below the VOL levels.

However, for LEDs unlike digital inputs of an exter-

nally connected device, they are not governed by

the same minimum VIH/VIL levels. An I/O pin out-

put can safely sink or source any current less than

that listed in the absolute maximum rating section

of the data sheet. For example:

VOH = 2.4v @ IOH = -8 mA and VDD = 3.3V

The maximum output current sourced by any 8 mA

I/O pin = 12 mA.

LED source current < 12 mA is technically

permitted. Refer to the VOH/IOH graphs in

Section 24.0 “Electrical Characteristics” for

additional information.

10.8

I/O Resources

Many useful resources are provided on the main prod-

uct page of the Microchip web site for the devices listed

in this data sheet. This product page, which can be

accessed using this link, contains the latest updates

and additional information.

10.8.1

KEY RESOURCES

• Section 10. “I/O Ports” (DS70193)

• Code Samples

• Application Notes

• Software Libraries

• Webinars

• All related dsPIC33F/PIC24H Family Reference

Manuals Sections

• Development Tools

Note:

Although it is not possible to use a digital

input pin when its analog function is

enabled, it is possible to use the digital I/O

output function, TRISx = 0x0, while the

analog function is also enabled. However,

this is not recommended, particularly if the

analog input is connected to an external

analog voltage source, which would cre-

ate signal contention between the analog

signal and the output pin driver.

Note:

In the event you are not able to access

the product page using the link above,

enter

this

URL

your

browser:

http://www.microchip.com/wwwproducts/

Devices.aspx?dDocName=en530334

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