Heinz Czychun wrote:
> With Timer 1 disabled I'm able to control Timer 0 effectively with the
> INTCON,T0IE bit. Off and on. But when I enable Timer 1, Timer 0 also
> starts up and starts interrupting the processor.
>
> Is this normal? Is it a known problem? Or am I missing something?

I'm guessing you aren't checking the IE bits for the disabled interrupts
so you get into a infinite interrupt if the IF bit for a disabled
interrupt gets set.

There are a number of issues with your code, however, before we can look at
that.  On the good side you seem to have paid attention to banking and did a
nice job of documenting bit settings.  That puts you ahead of 95% of newbies
already.  On the flip side there are some serious problems.  I didn't look
at the code in detail, so here is only what jumped out:

> ;***** VARIABLE DEFINITIONS
> #define LED_DS1 1            ;LED connected to GP1

This is not a variable at all.  You have defined a inline string
substitution macro.  They can be useful, but should only be used when really
needed.  If you just want to define a symbolic integer constant, do it right
and use EQU.  This isn't C.

> INT_VAR  UDATA_SHR 0x20

Bad idea.  I doubt you really need this to be specifically at location 20h,
so don't force it there.  This happens to work on this chip, but will
needless break on other chips that have the unbanked memory in a different
location.

> RESET_VECTOR CODE 0x000      ;processor reset vector
>          goto    main        ;go to beginning of program

This particular chip may have only one page, so you can get away with it
here, but that doesn't make it a good idea.  Use PAGESEL before the GOTO.
It won't emit code when the PIC only has a single page, but keeps this
from being a lurking bug if the code is ever moved to a larger PIC.

> INT_VECTOR CODE  0x004       ;interrupt vector location
>          goto    iServ

Never do this.  Some code will live at the interrupt vector, so it might as
well be the one routine that benefits from being there.  In addition, this
code is broken on any PIC with more than one page since it relies on PCLATH
at the time of the interrupt.  And no, using PAGESEL before the GOTO doesn't
fix it either because that corrupts PCLATH before the interrupt routine has
chance to save it.

> main

This should be in a separate section so that the linker can place it where
it wants to.  Right now your code actually forces it to be immediately after
the interrupt vector, which makes no sense.

>          movlw   b'00001000'
>          ;         0-------  1=disabled, no GPIO Pull-ups     GPPU: GPIO
Pull-ups
>          ;         -0------  0=falling edge interrupt,      INTEDG:
Interrupt Edge of GP2
>          ;         --0-----  0=Internal inst clock (CLKOUT),  T0CS: TMR0
Clock Source
>          ;         ---0----  0=Inc on lo^hi transition on GP2,T0SE: TMR0
Source Edge
>          ;         ----1---  1=Prescaler assigned to WDT,     PSA:
Prescaler Assignment
>          ;         -----0--  001 Prescaler 1:4,            PS2-PS0:
Prescaler Rate
>          ;         ------0-  Bits  TMR0    WDT
>          ;         -------0  000    1:2    1:1
>          ;                   001    1:4    1:2
>          ;                   010    1:8    1:4
>          ;                   011    1:16   1:8
>          ;                   100    1:32   1:16
>          ;                   101    1:64   1:32
>          ;                   110    1:128  1:64
>          ;                   111    1:256  1:128

The comment says 1:4 prescaler but the code says differently.  Since the
low 3 bits are all one field they should be documented as a single field,
not 3 individual bits.

>          bcf     INTCON, GIE

This makes no sense in the interrupt routine.  Read the manual.  GIE is
cleared by the hardware when the interrupt is taken, so this is a waste of
time.

>          btfsc   INTCON, T0IF
>          goto    ServiceTimer0
>          btfsc   PIR1, T1IF
>          goto    ServiceTimer1

Here is the cause of the symptoms I think.  As I guessed, you are jumping
to the interrupt service routines only if the IF bit is set and not
checking the IE bit.  That means that the timer 0 interrupt service
routine will be run even when its interrupt is disabled when you get here
for other reasons, which in this case is a timer 1 interrupt.


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