Interrupt 101

[HenrikOlsson]

Hi,
External interrupts are available on one or more pins. The 18F6520 seems to have four located on RB0-RB3. Smaller chips may only have one which is "always" on RB0. (Then you have the interrupt on change but lets leave that for now).

INTCON is the interrupt control register (one of them in the 18F6520). Look at the INTCON register in the datasheet, it'll show you what each bit does. In this case the MSB enables all unmasked interrupts and bit 4 enables the INT0 interrupt.

INTCON2.7=0 disables the internal pullup resistors for PortB.

The PBP is only part of the documentation, you must use the datasheet for your particular PIC as well.

Good luck!
/Henrik.

[Hylan]

Henrik,

I appreciate it. I've been looking at the datasheet and it's starting to make more sense. I'm not a programmer or circuit designer but am having to learn as this falls under the "other duties as deemed necessary" in the job description and the original guy who did it is no longer available.

So I think I now understand the physical input. Let's say I want to see an incoming serial message on pin RC7 (RX1 pin) and interrupt the home routine. I would need to first trigger RB0 to interrupt and goto the interrupt routine to read the serial data? Am I thinking correctly?

Second question. How do I set up software interrupts? Like if a certain value occurs like 3 I/O's are turned on then I want a variable like "AllON = 1" to interrupt the routine and do something.
Thank you,
Hylan

[mister_e]

There's USART interrupt as well. Check out the USART/EUSART section of the datasheet.

A really easy and efficient way to start right now with interrupts is to use Darrel Taylor Instant Interrupts. Check out this link.
http://www.pbpgroup.com/modules/wfse...p?articleid=19

For your, and any, specific requirement, there's a load of different approach.. say one different per programmer

The basic skelleton:
Main program (Loop)
Interrupts.

Whatever happen in your Interrupts, you may set flags there and process them in your main loop.

OR you may process some dull duties in your main loop and force interrupts to happen in your main loop too.

To read I/Os and evaluate them, you may use something like that (Which assume some push button connected to gnd on PORTB<3:0> (b3, b2, b1, b0)

SomePushButton VAR BYTE
'
'
'
'
SomePushButton = PORTB & $0F ' read PORTB and keep only <3:0> bits (Bitwise AND)
SELECT CASE SomePushButton
     CASE %1110 ' PORTB.0
          ' code for PORTB.0 here
     CASE %1101 ' PORTB.1
          ' code for PORTB.1 here
     CASE %1011 ' PORTB.2
          ' code for PORTB.2 here
     CASE %0111 ' PORTB.3
          ' code for PORTB.3 here
     END SELECT

[Hylan]

Beautifull! I feel like I now have enough to be dangerous or at least dangerous in a productive, 'hmmm that didn't work but I learned something' sort of way.

Thank goodness for reprogrammable pics!

Thank you,
Hylan

[mister_e]

Thank goodness for reprogrammable pics!

Amen! Couldn't even think to re-use my UV Eraser anyway

I still have some UV one though... good on a pinboard or as staple... (again)

if someone talk about software simulator I'll kick his butt

[Charles Linquis]

And most people don't realize it, but you can have an interrupt on *ANY* pin - sort of. This is handy when you have a switch that simply must be read and it is on port C, for example.
Just run a high-speed interrupt on TMR0 and read whatever pins you want inside the ISR. I typically run a 1mSec interrupt.

A small example of an "interrupt header"

 
  PreloadH      VAR BYTE BANKA SYSTEM
  PreloadL       VAR BYTE BANKA SYSTEM
  MasterClock   VAR WORD BANKA SYSTEM
  ButtonFlag    var BYTE BANKA SYSTEM
 
 
  PreloadH= $D8
  PreloadL = $F7    ; 1 mSec@40Mhz
 
  T0CON = %10001000  ; Timer ON, no prescaler
 
 
'---------------------------------- --------------------------------  
 
        INCLUDE "DT_INTS-18.bas"         
 
'        INCLUDE "ReEnterPBP-18.bas"     ; Include if using PBP interrupts
 
ASM
INT_LIST  macro    ;IntSource,        Label,  Type, ResetFlag?
 
     INT_Handler    TMR0_INT,   MainTimer, ASM,  yes 
; INT_Handler    RX1_INT, GetChar,    PBP,  yes
 
endm
 
INT_CREATE               
 
ENDASM
 
Goto OverInt
 
 
'---[INT - interrupt handler]---------------------------------------------------
 
Asm                            
 
MainTimer
 
    movff    PreloadH,TMR0H  ; Preload depends on clk speed
    movff    PreloadL,TMR0L
     clrf     INTCON,2
 
     infsnz  MasterClock
     incf    MasterClock + 1
 
     btfss  PORTC,4
     bsf  ButtonFlag,0
 
@ INT_RETURN
 
ENDASM      
 
OverInt:
 
   ButtonFlag = 0
   MasterClock = 0
   INTCON =%11100000  ; just to be certain!
 
@ INT_ENABLE TMR0_INT  
 
 
Your program here

This particular code will increment MasterClock at a 1000Hz rate (1 ms / count). You can read it at any time, although you should either disable INTs when you test it, or only test that it is ABOVE (not equal to) a value, since it is a 16 bit var and can increment in the middle of a PBP read.

ButtonFlag.0 will be set any time after someone has pressed a button bringing PORTC.4 to GND. You can read it anytime, then clear it in your main code.

If you have more complicated things to do on an interrupt, you can write it in PBP.


So THERE! mister_e and pxidr84!

[amgen]

That's a good setup !
How about switch de-bounce (make sure its a good press)

I use;

if sw not_pressed then out
pause 10 ' or 20 or 50 ms
if sw not_pressed then out
good sw pressed stuff here

don

[mister_e]

And most people don't realize it, but you can have an interrupt on *ANY* pin - sort of. ........
So THERE! mister_e and pxidr84!

Sure, I classify that as slow background process

amgen, you just need to read the switch all the time, keep a reading of the previous(s) and compare them. Depending of your timer rate, you may want to make sure it is hold down for X interrupt. set a flag to say a switch is ready, Once done, and the button being read, you wait Y interrupt before reading another and "publish" it.

Tons of way to do so. But for sure, you don't want any PAUSE in an ISR.