Can I have interupts on any pin ?

[Charles Linquis]

This is an example of what I mentioned earlier.

I'll call it FAKE INTERRUPT

It does have a latency of a little over a millisecond, but often it is plenty good enough to do what you need done. You can make the interrupt faster if you wish - but remember each time you enter/leave an interrupt, you are stealing quite a few processor cycles.


This code will check the status of any pin once per millisecond. It was written for an 18Fxxxx at 40Mhz. This example is checking the status of PORTC.0.

    Changed VAR BYTE
     OldPort VAR BYTE
      
     T0CON = %10001000 ; turn it on, 16 bits, no prescaler (osc/4)
        
     CLEAR 


'-----------------  DT_INTS section ----------------------------        
       
        INCLUDE "DT_INTS-18.bas"        
        INCLUDE "ReEnterPBP-18.bas"     
ASM
     INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
              INT_Handler    TMR0_INT,   _FakeInt,   PBP,  yes 
          endm
    INT_CREATE           
ENDASM


Goto OverInt

'------------------ Timer 0 interrupt handler-----------------------------------


FakeInt:
        
         TMR0H = $D8  ; Preload depends on clk speed
         TMR0L = $F7  ; One millesecond timeout at 40Mhz. 
                      ; Always load HIGHBYTE FIRST
                              
         Changed = PortC ^ OldPort 
         IF Changed.0 = 1 THEN     ; Pick your pin
             OldPort = PortC
             ;;;;  Whatever you want to do when Port bit changes
         ENDIF     
         
@ INT_RETURN         


Overint:
  
  OldPort = PortC    ; Init the var

@ INT_ENABLE TMR0_INT


NormalProgramLoop:

   

    Goto NormalProgramLoop
   
  END

[Bruce]

Here's a schematic for 13 pins with interrupts using just two interrupt-on-change pins.

[sayzer]

Here's a schematic for 13 pins with interrupts using just two interrupt-on-change pins.

At Post#3, I was trying to explain the same method.

--------------------------

[Bruce]

At Post#3, I was trying to explain the same method.

That's what reminded me I had the schematic...;o)

[Bonxy]

WoW guys & gals, im overwhelmed with the response to this, thank you all very much.
Some of your ideas I have considdered, like a diode to the B0 pin, but I dont think that would work for my app, I need to have as many pins as input as possible which i think is about 33 at most on the 18f4550 (and 2 pins could fire at the same time), I will take a closer look at some of your suggestions on my day off work, it looks like some of it involves assembler which I dont get :-(, but Im sure I will pick something out of your ideas :-), Im just wondering if just polling the pins would be fast enough @ 20mhz, I'm gonna give all your ideas a try this w/end and see what works, thx

[Bonxy]

Just an afterthought,
do all pic micro ports/pins have internal pull up resistors ?, i've been looking at the 18f4550 datasheet but cant tell ?, maybe i'm just stupid or tired lol :-)'

Thanks

[aratti]

No, internal pullups applys only to portB.

Al.

[sayzer]

No, internal pullups applys only to portB.

Al.

Some other PICs have pull-ups on PORTA, too. I was not aware of this fact until recently.
Edit: For example, 16F630.

.... (and 2 pins could fire at the same time....

What does it matter?
If one or the other interrupts, you will get into interrupt routine anyway whether two interrupts occur at the same time or not (which I think is very close to impossible !)

While you are in interrupt routine, check the status of all pins, then act based on each of their tasks.

Something like >

RB0_Int: 'we are now in interrupt routine.
A = 0
B = 0
C = 0
D = 0
..
....
.......
IF Pin1 = 0 THEN A = 1 ' Pin1 seems to be interrupted.
IF Pin2 = 0 THEN B = 3  'Ohh, Pin2 also seems to interrupted.
....
.......