Datasheet

 2005-2012 Microchip Technology Inc. DS39747F-page 107
PIC24FJ128GA010 FAMILY
10.0 I/O PORTS
All of the device pins (except VDD, VSS, MCLR and
OSC1/CLKI) are shared between the peripherals and
the parallel I/O ports. All I/O input ports feature Schmitt
Trigger inputs for improved noise immunity.
10.1 Parallel I/O (PIO) Ports
A parallel I/O port that shares a pin with a peripheral is,
in general, subservient to the peripheral. The periph-
eral’s output buffer data and control signals are
provided to a pair of multiplexers. The multiplexers
select whether the peripheral or the associated port
has ownership of the output data and control signals of
the I/O pin. The logic also prevents “loop through”, in
which a port’s digital output can drive the input of a
peripheral that shares the same pin. Figure 10-1 shows
how ports are shared with other peripherals and the
associated I/O pin to which they are connected.
When a peripheral is enabled and the peripheral is
actively driving an associated pin, the use of the pin as
a general purpose output pin is disabled. The I/O pin
may be read, but the output driver for the parallel port
bit will be disabled. If a peripheral is enabled, but the
peripheral is not actively driving a pin, that pin may be
driven by a port.
All port pins have three registers directly associated
with their operation as digital I/O. The Data Direction
register (TRISx) determines whether the pin is an input
or an output. If the data direction bit is a ‘1’, then the pin
is an input. All port pins are defined as inputs after a
Reset. Reads from the latch (LATx), read the latch.
Writes to the latch, write the latch. Reads from the port
(PORTx), read the port pins, while writes to the port
pins, write the latch.
Any bit and its associated data and control registers
that are not valid for a particular device will be
disabled. That means the corresponding LATx and
TRISx registers, and the port pin will read as zeros.
When a pin is shared with another peripheral or func-
tion that is defined as an input only, it is nevertheless,
regarded as a dedicated port because there is no
other competing source of outputs. An example is the
INT4 pin.
FIGURE 10-1: BLOCK DIAGRAM OF A TYPICAL SHARED PORT STRUCTURE
Note: This data sheet summarizes the features
of this group of PIC24F devices. It is not
intended to be a comprehensive refer-
ence source. Refer to Section 12. “I/O
Ports with Peripheral Pin Select (PPS)”
(DS39711) in the “PIC24F Family
Reference Manual” for more information.
QD
CK
WR LAT +
TRIS Latch
I/O Pin
WR PORT
Data Bus
QD
CK
Data Latch
Read PORT
Read TRIS
1
0
1
0
WR TRIS
Peripheral Output Data
Output Enable
Peripheral Input Data
I/O
Peripheral Module
Peripheral Output Enable
PIO Module
Output Multiplexers
Output Data
Input Data
Peripheral Module Enable
Read LAT