Datasheet

PIC24FV16KM204 FAMILY
DS30003030B-page 140  2013 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 PIC24FXXXXX 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
37 external signals (CN0 through CN36) that may be
selected (enabled) for generating an interrupt request
on a Change-of-State.
There are six control registers associated with the CN
module. The CNEN1 and CNEN3 registers contain the
interrupt enable control bits for each of the CNx input
pins. Setting any of these bits enables a CN interrupt
for the corresponding pins.
Each CNx 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 CNPU3 registers,
which contain the control bits for each of the CNx 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 CNPD3
registers, which contain the control bits for each of the
CNx 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 (CN) 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.
{
}