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 mismatch
 
 // 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