Instant Interrupts - Revisited

[Darrel Taylor]

Chris,

The prescaler can be changed with T1CON.
$31 = 1:8
$21 = 1:4
$11 = 1:2
$01 = 1:1

And the Timer is reloaded by putting values in TMR1H:TMR1L.

So first, decide what frequency you need, I'll go with 100hz.

Then, go to this thread...
Testing Forms [TimerCalc] Working I think?
http://www.picbasic.co.uk/forum/showthread.php?t=2031

Enter the OSC value you are using, say 20mhz.
I'll also go with 1:1 prescaler, enter that. (ok, it's already there)
Then enter 100 in the Freq field at the bottom.

Now you can see that it will take a total of 50,000 counts (ticks) to achieve 100hz.

Decide what resolution you want for the Duty-Cycle. ummm, 8-bit (256).

Now you just calculate the ON count from that with...
50000*DutyCycle/256 which is the same thing as...
50000*/DutyCycle in PBP
and the OFF count is 50000 - ONcount

Ok, so let's put that into the Blinky Light example

; Initialize your hardware first.


INCLUDE "DT_INTS-18.bas"     ' Base Interrupt System
INCLUDE "ReEnterPBP-18.bas"     ' Include if using PBP interrupts


LED1       VAR PORTB.1
DutyCycle  VAR BYTE


TotalCount CON 50000
ONcount    VAR WORD
OFFcount   VAR WORD


ASM
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler   TMR1_INT,  _ToggleLED1,   PBP,  yes
    endm
    INT_CREATE               ; Creates the interrupt processor
ENDASM


T1CON = $00                ; Prescaler=1:1, TMR OFF
@ INT_ENABLE  TMR1_INT     ; enable Timer 1 interrupts


Main:
    FOR DutyCycle = 0 TO 255           ; Ramp up
        GOSUB  SetDutyCycle
        PAUSE  5
    NEXT DutyCycle


    FOR DutyCycle = 254 TO 1 STEP -1   ; Ramp down
        GOSUB  SetDutyCycle
        PAUSE  5
    NEXT DutyCycle
GOTO Main




SetDutyCycle:
    ONcount = TotalCount*/DutyCycle
    OFFcount = TotalCount - ONcount
    IF DutyCycle = 0 THEN
        T1CON.0 = 0    ; turn off timer
        LOW  LED1      ; idle LOW
    ELSE
        T1CON.0 = 1    ; timer on if DutyCycle > 0
    ENDIF 
RETURN


DISABLE DEBUG
'---[TMR1 - interrupt handler]------------------------------------------------
@Timer1=TMR1L             ; map timer registers to a word variable
Timer1 VAR WORD EXT


ToggleLED1:
    IF LED1 THEN
        LOW LED1
        T1CON.0 = 0         ; stop the timer
        Timer1  = OFFcount  ; Load OFF count
        T1CON.0 = 1         ; start timer
    ELSE
        HIGH LED1
        T1CON.0 = 0         ; stop the timer
        Timer1  = ONcount   ; Load ON count
        T1CON.0 = 1         ; start timer
    ENDIF
@ INT_RETURN
ENABLE DEBUG

[Darrel Taylor]

OK, So once you try that, you'll realize that the RAMP is not linear.

It's more a function of the LED output than the PWM routine itself.

Changing it to 10-bit, and creating a lookup table that matches the LED brightness, seems to work. But I'm sure someone can come up with a better idea.
<br>

[Demon]

Darrel, if all goes well I hope to be able to commercialize this project within the next 57 years. Can I have your permission to include all this nice stuff within my code?

Hey, when I first started this project it was supposed to be nothing but a few switches and LEDs. That must have been over 2 years ago. Now I'm using a 320x240 graphic LCD, an 18F4550, two 16F628, 2 MCP23016, surface mount components, USB full speed, VB and eventually an Access database (I'm Tim The Toolman Taylor of home electronics).

Having to learn electronics kinda put me slightly behind schedule.

Robert
:lol:

[Darrel Taylor]

Hi Tim

If you do it in the next 57 days (or 5.7), you can still use everything to your hearts content.

Of course, you could add some routines to the pot.

Help keep the Internet Free!
<br>

[Demon]

Thank you, thank you, thank you, thank you, thank you!
Thank you, thank you, thank you, thank you, thank you!

You can be sure that I will post anything useful that I can contribute; like the stuff for the SED1335 graphic LCD. Last time I Googled, there were no code examples for that one.

But I'm afraid there's not much I can add; you, Mister E and the other regulars have already covered anything I could conjure (and then some).

Robert

[Darrel Taylor]

But I'm afraid there's not much I can add;

Well, I'm no philosophy major, but I figure...

The Day you decide you Can't, is also the Day you won't.

Give it a try.
Added: or should I say more tries (examples). (SED1335 320x240 graphic LCD)

DT

Oh, and, You're Welcome, You're Welcome, You're Welcome,
You're Welcome, You're Welcome, You're Welcome.

[Charles Linquis]

Darrel,

I'm trying to work your Instant Interrupts in to my regular code.

When compiling, I get the following error messages:

WARNING:Unable to fit variable RetAddrH in requested bank 16
WARNING:Unable to fit variable RetAddrL in requested bank 16
WARNING:Unable to fit variable INT_Flags in requested bank 16
WARNING:Unable to fit variable HP_Vars in requested bank 0


Since these are just warnings, do I need to be concerned?
Is there a solution?