PIC24FJ16MC101_12 Datasheet, PDF (120/350 Pages) Microchip Technology – 16-bit Microcontrollers (up to 32 KB Flash and 2 KB SRAM)

PIC24FJ16MC101/102 AND PIC24FJ32MC101/102/104
10.5 I/O Helpful Tips
1. In some cases, certain pins as defined in Table 26-10
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 external current limiting precau-
tions 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 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 VDD 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 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.
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.
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 ~(VDD-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
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 26.0 “Electrical Characteristics” for
additional information.
10.6 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.
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=en554339
10.6.1 KEY RESOURCES
• Section 12. “I/O Ports with Peripheral Pin Select
(PPS)” (DS39711)
• Code Samples
• Application Notes
• Software Libraries
• Webinars
• All related PIC24F Family Reference Manual
Sections
• Development Tools
DS39997C-page 120
Preliminary
© 2011-2012 Microchip Technology Inc.