Datasheet

dsPIC33FJ06GS001/101A/102A/202A and dsPIC33FJ09GS302
DS75018C-page 152  2011-2012 Microchip Technology Inc.
10.7 I/O Helpful Tips
1. In some cases, certain pins, as defined in
Table 25-9 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 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 respect to the V
SS 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 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 register in the ADC module
(i.e., ADPCFG) 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 configu-
rations 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
priorities of the functions allocated to any pins are
indicated by reading the pin name from left-to-right.
The left most function name takes precedence over
any function to its right in the naming convention; for
example: AN2/CMP1C/CMP2A/RA2. This indi-
cates that AN2 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 func-
tion 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
VDD. 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 Char-
acteristics specification. The respective I
OH and
IOL current rating only applies to maintaining the
corresponding 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 min-
imum V
IH/VIL levels. An I/O pin output can safely
sink or source any current less than that listed in
the “Absolute Maximum Ratings(1)” in
Section 25.0, Electrical Characteristics of this
data sheet. For example:
V
OH = 2.4V @ IOL = -6 mA and VDD = 3.3V
The maximum output current sourced by any
4x I/O pin = 15 mA.
LED source current <15 mA is technically permitted.
Refer to the V
OH/IOH graphs in Section 26.0 “DC
and AC Device Characteristics Graphs” for
additional information.
10.8 I/O Resources
Many useful resources related to I/O are provided on
the Microchip web site (www.microchip.com).
10.8.1 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.