PIC24FJ16MC101_12 Datasheet, PDF (116/350 Pages) Microchip Technology – 16-bit Microcontrollers (up to 32 KB Flash and 2 KB SRAM)

PIC24FJ16MC101/102 AND PIC24FJ32MC101/102/104
10.1.1 OPEN-DRAIN CONFIGURATION
In addition to the PORT, LAT, and TRIS registers for
data control, some port pins can also be individually
configured for either digital or open-drain output. This
is controlled by the Open-Drain Control register,
ODCx, associated with each port. Setting any of the
bits configures the corresponding pin to act as an
open-drain output.
The open-drain feature allows the generation of
outputs higher than VDD (e.g., 5V) on any desired 5V
tolerant pins by using external pull-up resistors. The
maximum open-drain voltage allowed is the same as
the maximum VIH specification.
See “Pin Diagrams” for the available pins and their
functionality.
10.2 Configuring Analog Port Pins
The AD1PCFG and TRIS registers control the opera-
tion of the analog-to-digital port pins. The port pins that
are to function as analog inputs must have their corre-
sponding TRIS bit set (input). If the TRIS bit is cleared
(output), the digital output level (VOH or VOL) will be
converted.
The AD1PCFGL register has a default value of 0x0000;
therefore, all pins that share ANx functions are analog
(not digital) by default.
When the PORT register is read, all pins configured as
analog input channels will read as cleared (a low level).
Pins configured as digital inputs will not convert an
analog input. Analog levels on any pin defined as a
digital input (including the ANx pins) can cause the
input buffer to consume current that exceeds the
device specifications.
10.2.1 I/O PORT WRITE/READ TIMING
One instruction cycle is required between a port
direction change or port write operation and a read
operation of the same port. Typically this instruction
would be an NOP. An demonstration is shown in
Example 10-1.
10.3 Input Change Notification
The input change notification function of the I/O ports
allows
the
PIC24FJ16MC101/102
and
PIC24FJ32MC101/102/104 devices to generate inter-
rupt requests to the processor in response to a change-
of-state on selected input pins. This feature can detect
input change-of-states even in Sleep mode, when the
clocks are disabled. Depending on the device pin
count, up to 31 external signals (CNx pin) can be
selected (enabled) for generating an interrupt request
on a change-of-state.
Four control registers are associated with the CN mod-
ule. The CNEN1 and CNEN2 registers contain the
interrupt enable control bits for each of the CN input
pins. Setting any of these bits enables a CN interrupt
for the corresponding pins.
Each CN pin also has a weak pull-up connected to it.
The pull-ups act as a current source connected to the
pin, and eliminate the need for external resistors when
push-button or keypad devices are connected. The
pull-ups are enabled separately using the CNPU1 and
CNPU2 registers, which contain the control bits for
each of the CN pins. Setting any of the control bits
enables the weak pull-ups for the corresponding pins.
Note:
Pull-ups on change notification pins
should always be disabled when the port
pin is configured as a digital output.
EXAMPLE 10-1: PORT WRITE/READ EXAMPLE
MOV
MOV
NOP
btss
0xFF00, W0
W0, TRISBB
PORTB, #13
; Configure PORTB<15:8> as inputs
; and PORTB<7:0> as outputs
; Delay 1 cycle
; Next Instruction
DS39997C-page 116
Preliminary
© 2011-2012 Microchip Technology Inc.