PORTB + PORTC Interrupt-On-Change

[Aussie Barry]

Of course!

http://au.element14.com/mill-max/090...83?Ntt=1279883

Cheers
Barry
VK2XBP

[Darrel Taylor]

Interrupts can be very useful for many different purposes ... this isn't one of them.
In fact, interrupts will only slow things down and reduce the resolution of your readings.

A variation of what Henrik was describing might look like this ...
The resolution with WORD variables for the counts is 9uS (16F1783 running at 32Mhz internal OSC).
If the counters are BYTEs, the resolution is 3.5 uS, as measured in the simulator.

With interrupts, using a BASIC language ISR, that resolution will suffer greatly.

DEFINE OSC 32

ANSELA = 0
ANSELB = 0

Results   VAR BYTE[9]
Res0      VAR Results[0]
Res1      VAR Results[1]
Res2      VAR Results[2]
Res3      VAR Results[3]
Res4      VAR Results[4]
Res5      VAR Results[5]
Res6      VAR Results[6]
Res7      VAR Results[7]
Res8      VAR Results[8]
IOCA      VAR BYTE
IOCB      VAR BYTE
Testing   VAR PORTC.0

IOCBP = $FF
IOCBF = 0

CLEAR
WHILE !Testing : WEND
PAUSE 20

WHILE Testing
    IOCA = IOCAF
    IOCAF = 0
    IOCB = IOCBF
    IOCBF = 0
    Res0 = Res0 + IOCA.0
    Res1 = Res1 + IOCA.1
    Res2 = Res2 + IOCA.2
    Res3 = Res3 + IOCA.3
    Res4 = Res4 + IOCA.4
    Res5 = Res5 + IOCA.5
    Res6 = Res6 + IOCB.0
    Res7 = Res7 + IOCB.1
    Res8 = Res8 + IOCB.2
WEND

[Aussie Barry]

HI All,

I am so glad I didn't show any of you my ISR code...it is embarrassing compared to what Darrel has just shared!

I also need to display results as they occur on a 4x20 LCD. There are two different display screens, one that gives a visual representation if a fault has occurred on any particular data line and another that displays actual fault counts for all nine lines. I don't know the timing requirements for LCDOUT statements but I am sure they will add considerably to the 9uS resolution with WORD variables. I could control the LCDOUT routine such that it only updates the LCD screen if a new fault has occurred. Is it possible to do a comparison using this pseudo-code:

Results VAR WORD[9]
OldResults VAR WORD[9]

IF Results <> OldResults THEN
Goto Display Routine ' break to the routine that updates the LCD screen
OldResults = Results ' Reset OldResults
ENDIF

Cheers
Barry
VK2XBP

[towlerg]

Hi Barry

1/. Towlerg: "Why not use a logic analyser?" - simply because I don't have one. I also need to replicate this test in other parts of the world so I don't think purchasing multiple logic analysers is a cost effective approach to solving the problem.

You can buy a Saleae for 119Euros. Accepted that you'll need an old laptop for display. It'll store billions of samples @ 24Mhz, thats at least a decade better that Darrel is suggesting, and he writes great code. How many samples before the PIC runs out of memory?

Anyways, good luck with the project.

George

[Aussie Barry]

Hi George,

Yes, there are always a number of different ways to "skin a cat" but if I went with the logic analyser route then I would have nothing to design and build using a PIC

If we end up with more than a byte's worth of fault counts on any of the nine data lines within a one minute test period then we have more problems to worry about than a PIC running out of memory!

Cheers
Barry
VK2XBP

[Aussie Barry]

Hi All,

I am still waiting for my PIC16F1783 chips to arrive so I have been doing some testing with a PIC16F1829.
I am getting good results but unsure if my code can be improved. Here is the stripped down version for comment.

' Connect LCD D4 to RC4 (Pin 6)
' Connect LCD D5 to RC5 (Pin 5)
' Connect LCD D6 to RC6 (Pin 8) 
' Connect LCD D7 to RC7 (Pin 9)
' Connect LCD RS to RC3 (Pin 7)
' Connect LCD E  to RC2 (Pin 14)
' Connect Data Line 1 to RA0 (Pin 19)
' Connect Data Line 2 to RA1 (Pin 18)
' Connect Data Line 3 to RA2 (Pin 17)
' Connect Data Line 4 to RA3 (Pin 4)
' Connect Data Line 5 to RA4 (Pin 3)
' Connect Data Line 6 to RA5 (Pin 2)
' Connect Data Line 7 to RB4 (Pin 13)
' Connect Data Line 8 to RB5 (Pin 12)
' Connect Data Line 9 to RB6 (Pin 11)

#CONFIG
        __config _CONFIG1, _FOSC_INTOSC & _WDTE_OFF & _MCLRE_OFF & _BOREN_OFF
        __config _CONFIG2, _PLLEN_ON & _LVP_OFF & _WRT_HALF
#ENDCONFIG

OSCCON = %11110000              ; Fosc = 32MHz
                                ; Clock determined by Fosc<1:0> Config Word
DEFINE OSC 32                   ; Define socillator as 32MHz

' Define LCD registers and bits
Define	LCD_DREG	PORTC
Define	LCD_DBIT	4
Define	LCD_RSREG	PORTC
Define	LCD_RSBIT	3
Define	LCD_EREG	PORTC
Define	LCD_EBIT	2
Define	LCD_BITS	4
Define	LCD_LINES	4
PAUSE 500               ' Pause to initialise LCD Display


' Define program variables
DisplayFlag var BIT
DisplayFlag = 0

Counter1    var BYTE
Counter2    var BYTE
Counter3    var BYTE
Counter4    var BYTE
Counter5    var BYTE
Counter6    var BYTE
Counter7    var BYTE
Counter8    var BYTE
Counter9    var BYTE
IOCA        var BYTE
IOCB        var BYTE

Counter1 = 0
Counter2 = 0
Counter3 = 0
Counter4 = 0
Counter5 = 0
Counter6 = 0
Counter7 = 0
Counter8 = 0
Counter9 = 0


ANSELA = 0                      ' Disable PORTA ADC
ANSELB = 0                      ' Disable PORTB ADC
ANSELC = 0                      ' Disable PORTC ADC
DACCON0.7 = 0                   ' Disable DAC
CM1CON0.7 = 0                   ' Disable comparator 1
CM2CON0.7 = 0                   ' Disable comparator 2
TRISC = %00000001               ' Set PORTC.0 and PORTC.1 as digital input
TRISA = %00111111               ' Set PORTA as digital inputs
TRISB = %01110000               ' Set PORTB.4-6 as digital inputs
OPTION_REG.7 = 0                ' Enable Weak Pull-ups
WPUA = %00111111                ' Pull-ups enabled on PORTA.0 - 5
WPUB = %01110000                ' Pull-ups enabled on PORTB.4 - 6
WPUC = %00000001                ' Enable PORTC.0 pull-ups

IOCAP = %00111111               ' Enable IOC rising edge on PORTA.0-5
IOCBP = %01110000               ' Enable IOC rising edge on PORTB.4-6
IOCAN = 0                       ' Disable IOC falling edge on PORTA
IOCBN = 0                       ' Disable IOC falling edge on PORTB


Main:
    IOCA = IOCAF                ' Save IOCAF to IOCA
    IOCB = IOCBF                ' Save IOCBF to IOCB
    IOCAF = 0                   ' Reset IOCAF
    IOCBF = 0                   ' Reset IOCBF
    IF IOCA > 0 OR IOCB > 0 THEN    ' Test if IOC Flags have changed
        DisplayFlag = 1             ' If so, set Display flag
    ENDIF
    Counter1 = Counter1 + IOCA.0
    Counter2 = Counter2 + IOCA.1
    Counter3 = Counter3 + IOCA.2
    Counter4 = Counter4 + IOCA.3
    Counter5 = Counter5 + IOCA.4
    Counter6 = Counter6 + IOCA.5
    Counter7 = Counter7 + IOCB.4
    Counter8 = Counter8 + IOCB.5
    Counter9 = Counter9 + IOCB.6
    IF DisplayFlag = 1 THEN         ' Go to Display subroutine if DisplayFlag set
        Gosub Display
        DisplayFlag = 0             ' Reset DisplayFlag
    ENDIF
GOTO Main

Display:
    LCDOUT $FE, $80, "    Fault Status    "
    LCDOUT $FE, $C0, "1. ", DEC3 Counter1, " 2. ", DEC3 Counter2, " 3. ", DEC3 Counter3
    LCDOUT $FE, $94, "4. ", DEC3 Counter4, " 5. ", DEC3 Counter5, " 6. ", DEC3 Counter6
    LCDOUT $FE, $D4, "7. ", DEC3 Counter7, " 8. ", DEC3 Counter8, " E. ", DEC3 Counter9
Return

Any suggested improvements would be greatly appreciated.

Cheers
Barry
VK2XBP

[HenrikOlsson]

Hi Barry,
First suggestion is very minor but still, clear IOCAF immediately after reading it, ie

IOCA = IOCAF                ' Save IOCAF to IOCA
IOCAF = 0                   ' Reset IOCAF
IOCB = IOCBF                ' Save IOCBF to IOCB
IOCBF = 0                   ' Reset IOCBF

The longer the time is between reading it and clearing it is the bigger the risk of missing an "event" is. In this case, as I said, very minor but still.

Next suggestion is to really try to tweak the display routine. Measure how long it takes now, then tweak it and compare. You want to make it as quick as you possibly can.
With tweaking I mean things like not rewriting static information each update. Instead, write the static information ONCE and then only update/overwrite what's actually needs to be updated.

You could, for example, use the bits in IOCA and IOCB to determine which counters content actually needs updating on the display. A possible drawback of doing this is that the execution time of the routine isn't constant so it's hard to tell exactly how fast the system will be able to detects consecutive events on the same "line". At the very least, don't rewrite that [ Fault Status ] - waste of time ;-)

As the code is currently written, I think you can skip the DisplayFlag semaphore and just do

IF IOCA > 0 OR IOCB > 0 THEN    ' Test if IOC Flags have changed
    GOSUB Display
ENDIF

But you may have something else in there preventing you from doing that, I don't know.

Another possible option to flip it around and have the Display routine as part of your main code (with the flag indicating it needs updating) and then GOSUB the code that checks the interrupt flags. That way can insert a GOSUB at various places WITHIN the Display routine (and the rest of the main loop) in an effort to really catch multiple events on the same line.

/Henrik.