Datasheet

dsPIC33FJXXXGPX06A/X08A/X10A
DS70593D-page 164  2009-2012 Microchip Technology Inc.
11.2 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 V
DD (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 V
IH specification.
See the “Pin Diagrams” section for the available pins
and their functionality.
11.3 Configuring Analog Port Pins
The use of the ADxPCFGH, ADxPCFGL and TRIS
registers control the operation of the ADC port pins.
The port pins that are desired as analog inputs must
have their corresponding TRIS bit set (input). If the
TRIS bit is cleared (output), the digital output level (VOH
or VOL) is converted.
Clearing any bit in the ADxPCFGH or ADxPCFGL
register configures the corresponding bit to be an
analog pin. This is also the Reset state of any I/O pin
that has an analog (ANx) function associated with it.
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) can cause the
input buffer to consume current that exceeds the
device specifications.
11.4 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.
11.5 Input Change Notification
The input change notification function of the I/O ports
allows the dsPIC33FJXXXGPX06A/X08A/X10A
devices to generate 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 24 external signals (CN0 through CN23) that
can be selected (enabled) for generating an interrupt
request on a change-of-state.
There are four control registers associated with the CN
module. The CNEN1 and CNEN2 registers contain the
CN interrupt enable (CNxIE) 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 that is 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 weak pull-up
enable (CNxPUE) bits for each of the CN pins. Setting
any of the control bits enables the weak pull-ups for the
corresponding pins.
EXAMPLE 11-1: PORT WRITE/READ EXAMPLE
Note: In devices with two ADC modules, if the
corresponding PCFG bit in either
AD1PCFGH(L) and AD2PCFGH(L) is
cleared, the pin is configured as an analog
input.
Note: The voltage on an analog input pin can be
between -0.3V to (V
DD + 0.3 V).
Note: Pull-ups on change notification pins
should always be disabled whenever the
port pin is configured as a digital output.
MOV 0xFF00, W0 ; Configure PORTB<15:8> as inputs
MOV W0, TRISBB ; and PORTB<7:0> as outputs
NOP ; Delay 1 cycle
btss PORTB, #13 ; Next Instruction