DVR datasheet(128/416 Pages) MICROCHIP

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PIC24FJ256GA705 FAMILY

DS30010118D-page 128

 2016-2018 Microchip Technology Inc.

11.3

Interrupt-on-Change (IOC)

The Interrupt-on-Change function of the I/O ports

allows the PIC24FJ256GA705 family of devices to gen-

erate 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.

Interrupt-on-Change functionality is enabled on a pin

by setting the IOCPx and/or IOCNx register bit for that

pin. For example, PORTC has register names, IOCPC

and IOCNC, for these functions. Setting a value of ‘1’ in

the IOCPx register enables interrupts for low-to-high

transitions, while setting a value of ‘1’ in the IOCNx

Setting a value of ‘1’ in both register bits will enable

interrupts for either case (e.g., a pulse on the pin will

generate two interrupts). In order for any IOC to be

detected, the global IOC Interrupt Enable bit (IEC1<3>)

must be set, the PADCON<15> bit set (IOCON) and the

associated ISFx flag cleared.

When an interrupt request is generated for a pin, the

corresponding status flag (IOCFx register bit) will be

set, indicating that a Change-of-State occurred on that

pin. The IOCFx register bit will remain set until cleared

by writing a zero to it. When any IOCFx flag bit in a

given port is set, the corresponding IOCPxF bit in the

IOCSTAT register will be set. This flag indicates that a

change was detected on one of the bits on the given

port. The IOCPxF flag will be cleared when all

IOCFx<15:0> bits are cleared.

Multiple individual status flags can be cleared by writing

a zero to one or more bits using a Read-Modify-Write

operation. If another edge is detected on a pin whose

status bit is being cleared during the Read-Modify-

Write sequence, the associated change flag will still be

set at the end of the Read-Modify-Write sequence.

The user should use the instruction sequence (or

equivalent) shown in Example 11-1 to clear the

Interrupt-on-Change Status registers.

At the end of this sequence, the W0 register will contain

a zero for each bit for which the port pin had a change

detected. In this way, any indication of a pin changing

will not be lost.

Due to the asynchronous and real-time nature of the

Interrupt-on-Change, the value read on the port pins

may not indicate the state of the port when the change

was detected, as a second change can occur during

the interval between clearing the flag and reading the

port. It is up to the user code to handle this case if it is

a possibility in their application. To keep this interval to

a minimum, it is recommended that any code modifying

the IOCFx registers be run either in the interrupt

handler or with interrupts disabled.

Each Interrupt-on-Change (IOC) pin has both a weak

pull-up and a weak pull-down connected to it. The pull-

ups act as a current source connected to the pin, while

the pull-downs act as a current sink 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 IOCPUx registers (for pull-ups) and the

IOCPDx registers (for pull-downs). Each IOC pin has

individual control bits for its pull-up and pull-down. Set-

ting a control bit enables the weak pull-up or pull-down

for the corresponding pin.

EXAMPLE 11-1:

IOC STATUS READ/CLEAR IN ASSEMBLY

EXAMPLE 11-2:

PORT READ/WRITE IN ASSEMBLY

EXAMPLE 11-3:

PORT READ/WRITE IN ‘C’

Note:

Pull-ups and pull-downs on pins should

always be disabled whenever the pin is

configured as a digital output.

MOV

0xFFFF, W0

; Initial mask value 0xFFFF -> W0

XOR

IOCFx, W0

; W0 has '1' for each bit set in IOCFx

AND

IOCFx

; IOCFx & W0 ->IOCFx

MOV

0xFF00, W0

; Configure PORTB<15:8> as inputs

MOV

W0, TRISB

; and PORTB<7:0> as outputs

NOP

; Delay 1 cycle

BTSS

PORTB, #13

; Next Instruction

TRISB = 0xFF00;

// Configure PORTB<15:8> as inputs and PORTB<7:0> as outputs

Nop();

// Delay 1 cycle

If (PORTBbits.RB13){ };

// Next Instruction

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