PIC24FJ256GB110-I Datasheet, PDF (124/328 Pages) Microchip Technology – 64/80/100-Pin, 16-Bit Flash Microcontrollers with USB On-The-Go (OTG)

PIC24FJ256GB110 FAMILY
9.1.1 OPEN-DRAIN CONFIGURATION
In addition to the PORT, LAT and TRIS registers for
data control, each port pin 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 con-
figures 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
digital only pins by using external pull-up resistors. The
maximum open-drain voltage allowed is the same as
the maximum VIH specification.
9.2 Configuring Analog Port Pins
The AD1PCFGL and TRIS registers control the opera-
tion of the A/D port pins. Setting a port pin as an analog
input also requires that the corresponding TRIS bit be
set. If the TRIS bit is cleared (output), the digital output
level (VOH or VOL) will be converted.
When reading the PORT register, 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 that is defined as
a digital input (including the ANx pins) may cause the
input buffer to consume current that exceeds the
device specifications.
9.2.1 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 a NOP.
9.3 Input Change Notification
The input change notification function of the I/O ports
allows the PIC24FJ256GB110 family of devices to gen-
erate interrupt requests to the processor in response to
a change of state on selected input pins. This feature is
capable of detecting input change of states even in
Sleep mode, when the clocks are disabled. Depending
on the device pin count, there are up to 81 external
inputs that may be selected (enabled) for generating an
interrupt request on a change of state.
Registers CNEN1 through CNEN6 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 has a both a weak pull-up and a weak
pull-down connected to it. The pull-ups act as a current
source that is connected to the pin, while the
pull-downs act as a current sink that is connected to the
pin. These eliminate the need for external resistors
when push button or keypad devices are connected.
The pull-ups and pull-downs are separately enabled
using the CNPU1 through CNPU6 registers (for
pull-ups) and the CNPD1 through CNPD6 registers (for
pull-downs). Each CN pin has individual control bits for
its pull-up and pull-down. Setting a control bit enables
the weak pull-up or pull-down for the corresponding
pin.
When the internal pull-up is selected, the pin pulls up to
VDD – 0.7V (typical). Make sure that there is no external
pull-up source when the internal pull-ups are enabled,
as the voltage difference can cause a current path.
Note:
Pull-ups on change notification pins
should always be disabled whenever the
port pin is configured as a digital output.
EXAMPLE 9-1: 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
DS39897B-page 122
Preliminary
© 2008 Microchip Technology Inc.