Datasheet

 2011-2012 Microchip Technology Inc. DS70652E-page 145
dsPIC33FJ16(GP/MC)101/102 AND dsPIC33FJ32(GP/MC)101/102/104
10.5 I/O Helpful Tips
1. In some cases, certain pins, as defined in
Section 26.0 “Electrical Characteristics”,
Table 26-11 under “Injection Current”, have
internal protection diodes to V
DD and VSS. The
term, “Injection Current”, is also referred to as
“Clamp Current”. On designated pins, with suffi-
cient external 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 V
DD, with respect
to the VSS and VDD supplies. Note that when the
user application forward 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 V
DD and VSS
power rails, may affect the ADC accuracy by
four to six counts.
2. 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
digital 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 configure the Analog Pin Configuration
register in the ADC module (AD1PCFGL), 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.
3. 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 prece-
dence 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.
4. 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 ~(V
DD-0.8), not
V
DD. This is still above the minimum VIH of
CMOS and TTL devices.
5. When driving LEDs directly, the I/O pin can
source or sink more current than what is specified
in the V
OH/IOH and VOL/IOL DC characteristic
specification. The respective I
OH and IOL current
rating only applies to maintaining the correspond-
ing output at or above the VOH and at or below the
V
OL levels. However, for LEDs unlike digital
inputs of an externally connected device, they are
not governed by the same minimum VIH/VIL
levels. An I/O pin output can safely sink or source
any current less than that listed in the absolute
maximum rating section of the data sheet. For
example:
V
OH = 2.4v @ IOH = -6 mA and VDD = 3.3V
The maximum output current sourced by any 6 mA
I/O pin = 15 mA.
LED source current < 15 mA is technically
permitted. Refer to the V
OH/IOH specifications in
Section 26.0 “Electrical Characteristics” for
additional information.
10.6 I/O Resources
Many useful resources are provided on the main
product 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.
10.6.1 KEY RESOURCES
• “dsPIC33F/PIC24H Family Reference Manual”,
Section 10. “I/O Ports” (DS70193)
• Code Samples
• Application Notes
• Software Libraries
• Webinars
• All related “dsPIC33F/PIC24H Family Reference
Manual” 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
create 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 in your browser:
http://www.microchip.com/wwwproducts/
Devices.aspx?dDocName=en554109