Microchip Technology MA330028 Data Sheet
2011-2013 Microchip Technology Inc.
DS70000657H-page 181
dsPIC33EPXXXGP50X, dsPIC33EPXXXMC20X/50X AND PIC24EPXXXGP/MC20X
11.5
I/O Helpful Tips
1.
In some cases, certain pins, as defined in
, under “Injection Current”, have inter-
nal protection diodes to V
DD
and V
SS
. 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
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 V
DD
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
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 V
SS
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, configuring a pin as an
analog input pin automatically disables the digital
input pin buffer and any attempt to read the digital
input level by reading PORTx or LATx will always
return a ‘0’, regardless of the digital logic level on
the pin. 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 registers in the I/O ports
module (i.e., ANSELx) by setting the appropriate bit
that corresponds to that I/O port pin to a ‘0’.
(i.e., ANx) are always analog pins by default after
any Reset. Consequently, configuring a pin as an
analog input pin automatically disables the digital
input pin buffer and any attempt to read the digital
input level by reading PORTx or LATx will always
return a ‘0’, regardless of the digital logic level on
the pin. 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 registers in the I/O ports
module (i.e., ANSELx) by setting the appropriate bit
that corresponds to that I/O port pin to a ‘0’.
3.
Most I/O pins have multiple functions. Referring to
the device pin diagrams in this data sheet, the prior-
ities 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: AN16/T2CK/T7CK/RC1. This indi-
cates 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.
the device pin diagrams in this data sheet, the prior-
ities 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: AN16/T2CK/T7CK/RC1. This indi-
cates 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 pin has an internal weak pull-up resistor and
pull-down resistor that can be configured using the
CNPUx and CNPDx registers, respectively. These
resistors eliminate the need for external resistors
in certain applications. The internal pull-up is up to
~(V
pull-down resistor that can be configured using the
CNPUx and CNPDx registers, respectively. These
resistors eliminate the need for external resistors
in certain applications. The internal pull-up is up to
~(V
DD
– 0.8), not V
DD
. This value is still above the
minimum V
IH
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
or sink more current than what is specified in the
V
OH
/I
OH
and V
OL
/I
OL
DC characteristic specifica-
tion. The respective I
OH
and I
OL
current rating only
applies to maintaining the corresponding output at
or above the V
or above the V
OH
, and at or below the V
OL
levels.
However, for LEDs, unlike digital inputs of an
externally connected device, they are not gov-
erned by the same minimum V
externally connected device, they are not gov-
erned by the same minimum V
IH
/V
IL
levels. An I/O
pin output can safely sink or source any current
less than that listed in the absolute maximum
rating section of this data sheet. For example:
less than that listed in the absolute maximum
rating section of this data sheet. For example:
V
OH
= 2.4V @ I
OH
= -8 mA and V
DD
= 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 V
I/O pin = 12 mA.
LED source current < 12 mA is technically
permitted. Refer to the V
OH
/I
OH
graphs in
for
additional information.
6.
The Peripheral Pin Select (PPS) pin mapping rules
are as follows:
a) Only one “output” function can be active on a
are as follows:
a) Only one “output” function can be active on a
given pin at any time, regardless if it is a ded-
icated or remappable function (one pin, one
output).
icated or remappable function (one pin, one
output).
b)
It is possible to assign a “remappable output”
function to multiple pins and externally short or
tie them together for increased current drive.
function to multiple pins and externally short or
tie them together for increased current drive.
c)
If any “dedicated output” function is enabled
on a pin, it will take precedence over any
remappable “output” function.
on a pin, it will take precedence over any
remappable “output” function.
d) If any “dedicated digital” (input or output) func-
tion is enabled on a pin, any number of “input”
remappable functions can be mapped to the
same pin.
remappable functions can be mapped to the
same pin.
e) If any “dedicated analog” function(s) are
enabled on a given pin, “digital input(s)” of any
kind will all be disabled, although a single “dig-
ital output”, at the user’s cautionary discretion,
can be enabled and active as long as there is
no signal contention with an external analog
input signal. For example, it is possible for the
ADC to convert the digital output logic level, or
to toggle a digital output on a comparator or
ADC input provided there is no external
analog input, such as for a built-in self-test.
kind will all be disabled, although a single “dig-
ital output”, at the user’s cautionary discretion,
can be enabled and active as long as there is
no signal contention with an external analog
input signal. For example, it is possible for the
ADC to convert the digital output logic level, or
to toggle a digital output on a comparator or
ADC input provided there is no external
analog input, such as for a built-in self-test.
f)
Any number of “input” remappable functions
can be mapped to the same pin(s) at the same
time, including to any pin with a single output
from either a dedicated or remappable “output”.
can be mapped to the same pin(s) at the same
time, including to any pin with a single output
from either a dedicated or remappable “output”.
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.
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.