Spency's digital-diy 18F PIC micro Tutorial

18F Code Snippet - Interrupt PORTB

PORTB interrupts are used for instantaneous response for changes to Pins 7, 6, 5, 4 on PORTB. Further more, the interrupt will even wake the PIC from a Sleep instruction, so your device can be in low power mode (the PIC can draw as low as 0.1u Amps while in Sleep mode), and be instantly awoken when there is a change on PORTB.

One precaution to be aware of is to Read the contents of PORTB within the ISR (Interrupt Service Routine). This is a hardware requirement to clear the mismatch condition that triggers the PORTB interrupt flag. The following program shows how to create a PORTB interrupt routine, that puts the PIC to Sleep after enabling the interrupt, and upon any pin change on PORTB 7:4, the PIC will wake up (thanks to the PORTB interrupt) and the change will be mirrored to PORTC.

Note the PIC's power supply/oscillator are not shown

Click here to watch this circuit in action

Device = 18F452
Clock = 20

Dim 
    RBIF As INTCON.0,
    RBIE As INTCON.3
    
Interrupt PORTB_Change()
    Save(0)                                   // Save the system variables
    If RBIF = 1 Then                          // Check if the interrupt was a PORTB change
	RBIF = 0
        WREG = PORTB                          // Be sure to read the contents of PORTB to clear the missmatch
        // PORTB 7:4 has changed, do what you want here...
        PORTC = PORTB                         // In this case, I am making PORTC = PORTB
    EndIf
    Restore                                   // Restore the system variables
End Interrupt

Sub PORTB_Interrupts(Control As Boolean)      // Small routine to enable/disable PORTB Interrupts.
    If Control = True Then                    //
        RBIE = 1                              //
        Enable(PORTB_Change)                  //
    Else                                      //
        RBIE = 0                              //
        Disable(PORTB_Change)                 //
    EndIf                                     //
End Sub

Inline Sub Sleep()
   ASM
   Sleep
   End ASM
End Sub 

// Start Of Program...
TRISB = %11110000                             // Make PORTB7:4 all inputs
TRISC = %00000000                             // Make PORTC all outputs

PORTB_Interrupts(True)                        // Enable PORTB interrupts

While True                                    // Infinite loop
    Sleep                                     // Put the PIC to sleep and wait for a change on PORTB 7:4
Wend