6.4.1.7 Input Change Notification (CN)

The Input Change Notification (CN) function of the I/O ports allows PIC32CX-BZ3 devices to generate interrupt 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 the Sleep mode, when the clocks are disabled.

The following control registers are associated with the CN functionality of each I/O port:

Change Notice Pull-up Enable (CNPUEx)
Change Notice Pull-down Enable (CNPDx)
Change Notice Control (CNCONx)
Change Notice Enable (CNENx/CNNEx)
Change Notice Status (CNSTATx/CNFx) or the positive edge control

Each I/O pin also has a weak pull-up and a weak pull-down connected to it. The pull-ups act as a current source or sink source connected to the pin and eliminate the need for external resistors when push button or keypad devices are connected. The pull-ups and pull-downs are enabled separately using the CNPUEx and the CNPDx registers, which contain the control bits for each of the pins. Setting any of the control bits enables the weak pull-ups and/or pull-downs for the corresponding pins.

Note: Pull-ups and pull-downs on change notification pins must always be disabled when the port pin is configured as a digital output

The CNCONx registers provide change notice control.

The CNENx/CNNEx registers contain the CN interrupt enable control bits for each of the input pins. Setting any of these bits enables a CN interrupt for the corresponding pins. CNENx enables a mismatch CN interrupt condition when EDGEDETECT is not set. When EDGEDETECT is set, CNNEx controls the negative edge while CNENx controls the positive. On devices that do not have EDGEDETECT, this CN logic acts as if EDGEDETECT is not set.

The CNSTATx/CNFx registers indicate whether a change occurred on the corresponding pin since the last read of the PORTx bit. The CNFx registers indicate the type of change that occurred.