Making a timer, 32.768kHz+555+DT_INT. Good idea?

[Darrel Taylor]

Hmmm, apparently the Timer1 oscillator doesn't work.

Instead ... exclude the crystal and caps from the simulation, and add a clock generator on the T1OSI input.



Set it up like this.

[financecatalyst]

Thank you so much for helping me reaching near the completion this project.
Adding the external clock as per the above image, has not solved the problem, I will need to check it on a real hardware from now on. Few last questions please:
1) Please explain my earlier question, that as soon as the interrupt happens, what exactly is happening, my understanding upto now says (please correct me if I am wrong):-
a) Few registers are saved [Which takes some time - Now, I have 15 byte variables, 2 Bit variables & 4 alias for 4 port pins - How do I calculate the exact delay & come up with a value to load into timer1 so I get perfect 1 sec intervals] (my pic is also running on 32.768kHz)
b) As soon as the first instruction is executed in the ISR, does timer1 keeps the value 0 in it untill ISR is executed in full OR it starts incrementing straightaway regardless if it is in ISR or main code. The latter makes more sense to me as I think thats why you advised to reload it as a first instruction in the ISR.

Please help me find answers to the above and hence get perfect 1 sec intervals.

[Darrel Taylor]

The timer continues counting no matter what the program is doing.

And yes, it does take time to save all the PBP system registers before it gets to the interrupt handler.
But that has no affect on the reload value.

Your problem before was that you were overwriting the timers value with TMR1L = 0.

Here is the program I used with the Digital Clock Generator shown above, and it does keep perfect time.

;--------------------------------------------------------------
wsave        VAR BYTE $70 SYSTEM
INCLUDE "DT_INTS-14.bas"     ; Base Interrupt System
INCLUDE "ReEnterPBP.bas"     ; Include if using PBP interrupts

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

@   INT_ENABLE   TMR1_INT     ; enable external (INT) interrupts
;--------------------------------------------------------------
Sec          VAR BYTE
Minute       VAR BYTE
Hour         VAR BYTE
SecChanged   VAR BIT

;--------------------------------------------------------------
ADCON1 = 7
TMR1L = 0
TMR1H = $80
T1CON = %00001011
PAUSE 250
LCDOUT $FE,1

;--------------------------------------------------------------
Main:
    IF SecChanged THEN
        SecChanged = 0
        LCDOUT $FE,$80, DEC2 Hour,":",DEC2 Minute,":",DEC2 Sec 
    ENDIF
GOTO Main

;--------------------------------------------------------------
Clock:
    TMR1H.7 = 1
    Sec = Sec + 1
    SecChanged = 1
    IF Sec = 60 THEN Sec = 0 : Minute = Minute + 1
    IF Minute = 60 THEN Minute = 0 : Hour = Hour + 1
    IF Hour = 24 THEN Hour = 0
@ INT_RETURN

[financecatalyst]

Thank you very much Darrel. Surely learnt something new in this project.

So, even when variables are getting saved before entering ISR, only lower bit of timer one is getting incremented in that time. Previously I was resetting it again to '0', which I shouldn't do and let it increment to keep it in sync. BUT it does not reach to higher bit of timer1 in such short time, so we only put TMR1H.7=1, which keep everything simple and in sync.

That is why you also said that in my code it does not matter if that statement is in the beginning of the code or end, because the increment does not reach that higher value even after executing some statements in my ISR.

Got it now (Atleast I hope I have this concept cleared FOREVER)

[Darrel Taylor]

Excellent!

Now you really have "Got It".
And described it well.

Cheers,

[financecatalyst]

I made my circuit on my breadboard. It works kind of OK (INT are longer than 1 sec intervals) with TICON=%00001111 the clock still keeps incrementing even when I take out the 32KHz crystal from RC0-RC1.

The clock stops with
TICON=%00001011, seems Interrupts stop happening with this setting. Can someone please put some light on why this could be happening?

[financecatalyst]

Anyone? Should I start a new thread with this problem?