Datasheet

 2013-2014 Microchip Technology Inc. DS70000689D-page 173
dsPIC33EPXXXGM3XX/6XX/7XX
11.5 High-Voltage Detect
The dsPIC33EPXXXGM3XX/6XX/7XX devices contain
High-Voltage Detection (HVD) which monitors the V
CAP
voltage. The HVD is used to monitor the VCAP supply
voltage to ensure that an external connection does not
raise the value above a safe level (~2.4V). If high core
voltage is detected, all I/Os are disabled and put in a
tri-state condition. The device remains in this I/O tri-
state condition as long as the high-voltage condition is
present.
11.6 I/O Helpful Tips
1. In some cases, certain pins, as defined in
Table 33-10 under “Injection Current”, have inter-
nal 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 rat-
ings, 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, 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
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: AN16/T2CK/
T7CK/RC1. This indicates that AN16 is the high-
est 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, respec-
tively. These resistors eliminate the need for
external resistors in certain applications. The
internal pull-up is up to ~(V
DD – 0.8), not VDD.
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
OH/IOH and VOL/IOL DC charac-
teristic specifications. The respective I
OH and
I
OL current rating only applies to maintaining the
corresponding output at 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 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 rating section of this data
sheet. For example:
V
OH = 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 V
OH/IOH graphs in
Section 33.0 “Electrical Characteristics” for
additional information.
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.