Datasheet

PIC24FV32KA304 FAMILY
DS30009995E-page 138  2011-2017 Microchip Technology Inc.
11.2.2 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.
11.3 Input Change Notification (ICN)
The Input Change Notification function of the I/O ports
allows the PIC24FV32KA304 family of devices to
generate interrupt requests to the processor in
response to a Change-of-State (COS) 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 23 external signals (CN0 through
CN22) that may be selected (enabled) for generating
an interrupt request on a Change-of-State.
There are six control registers associated with the ICN
module. 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/pull-down
connected to it. The pull-ups act as a current source
that is connected to the pin. The pull-downs act as a
current sink to eliminate the need for external resistors
when push button or keypad devices are connected.
On any pin, only the pull-up resistor or the pull-down
resistor should be enabled, but not both of them. If the
push button or the keypad is connected to V
DD , enable
the pull-down, or if they are connected to V
SS , enable
the pull-up resistors. 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. The pull-downs are
enabled separately, using the CNPD1 and CNPD2 reg-
isters, which contain the control bits for each of the CN
pins. Setting any of the control bits enables the weak
pull-downs for the corresponding pins.
When the internal pull-up is selected, the pin uses V
DD
as the pull-up source voltage. When the internal
pull-down is selected, the pins are pulled down to V
SS
by an internal resistor. Make sure that there is no
external pull-up source/pull-down sink when the
internal pull-ups/pull-downs are enabled.
EXAMPLE 11-1: PORT WRITE/READ EXAMPLE
Note: Pull-ups and pull-downs on Change Notifi-
cation pins should always be disabled
whenever the port pin is configured as a
digital output.
MOV 0xFF00, W0; //Configure PORTB<15:8> as inputs and PORTB<7:0> as outputs
MOV W0, TRISB;
NOP; //Delay 1 cycle
BTSS PORTB, #13; //Next Instruction
Equivalent ‘C’ Code
TRISB = 0xFF00; //Configure PORTB<15:8> as inputs and PORTB<7:0> as outputs
NOP(); //Delay 1 cycle
if(PORTBbits.RB13 == 1) // execute following code if PORTB pin 13 is set.
{
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