Datasheet

 2010 Microchip Technology Inc. DS39951C-page 121
PIC24FJ64GA104 FAMILY
10.0 I/O PORTS
All of the device pins (except VDD, VSS, MCLR and
OSCI/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 peripheral’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 out-
put 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/Os. The Data Direction
register (TRIS) 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 Output Latch register (LAT),
read the latch. Writes to the Output Latch register, write
the latch. Reads from the port (PORT), 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 LAT and
TRIS 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 regarded as a
dedicated port because there is no other competing
source of outputs.
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 reference
source. For more information, refer to the
“PIC24F Family Reference Manual”,
Section 12. “I/O Ports with Peripheral
Pin Select (PPS)” (DS39711).
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