PIC24FJ64GA104 FAMILY
When a peripheral is enabled and the peripheral is
actively driving an associated pin, the use of the pin as
10.0 I/O PORTS
Note:
This data sheet summarizes the features
of this group of PIC24F devices. It is not
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.
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).
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.
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.
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
Peripheral Module
Output Multiplexers
Peripheral Input Data
Peripheral Module Enable
Peripheral Output Enable
Peripheral Output Data
I/O
1
0
Output Enable
Output Data
1
0
PIO Module
Read TRIS
Data Bus
WR TRIS
D
Q
I/O Pin
CK
TRIS Latch
D
Q
WR LAT +
WR PORT
CK
Data Latch
Read LAT
Input Data
Read PORT
2010 Microchip Technology Inc.
DS39951C-page 121
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