> I prefer to specify individual bits like this, but leave bit fields (such
> as the three prescaler bits here) in binary, as in:
>
>  movlw  1<<TMR0ON | b'101'<<T0PS0   ; turn on TMR0, prescale = 64


You can make it even complicated:


ON     equ    1
OFF    equ    0

_T0CON = 0

TMR0     macro    s
            if s == ON
_T0CON |= 1<<TMR0ON
                exitm
            endif
            if s==OFF
_T0CON &= ~(1<<TMR0ON)
                exitm
            endif

        error Invalid parameter to TMR0 macro s
        endm

T0PS     macro    s
_T0CON &= ~(1<<T0PS2 | 1<<T0PS1 | 1<<T0PS0)
_T0CON |= (1<<PSA)
            if s == .1
                exitm
            endif
            if s == .2
_T0CON &= ~(1<<PSA)
_T0CON |= (0<<T0PS2) | (0<<T0PS1) | (0<<T0PS0)
                exitm
            endif
            if s == .4
_T0CON &= ~(1<<PSA)
_T0CON |= (0<<T0PS2) | (0<<T0PS1) | (1<<T0PS0)
                exitm
            endif
            if s == .8
_T0CON &= ~(1<<PSA)
_T0CON |= (0<<T0PS2) | (1<<T0PS1) | (0<<T0PS0)
                exitm
            endif
            if s == .16
_T0CON &= ~(1<<PSA)
_T0CON |= (0<<T0PS2) | (1<<T0PS1) | (1<<T0PS0)
                exitm
            endif
            if s == .32
_T0CON &= ~(1<<PSA)
_T0CON |= (1<<T0PS2) | (0<<T0PS1) | (0<<T0PS0)
                exitm
            endif
            if s == .64
_T0CON &= ~(1<<PSA)
_T0CON |= (1<<T0PS2) | (0<<T0PS1) | (1<<T0PS0)
                exitm
            endif
            if s == .128
_T0CON &= ~(1<<PSA)
_T0CON |= (1<<T0PS2) | (1<<T0PS1) | (0<<T0PS0)
                exitm
            endif
            if s == .256
_T0CON &= ~(1<<PSA)
_T0CON |= (1<<T0PS2) | (1<<T0PS1) | (1<<T0PS0)
                exitm
            endif

        error Invalid parameter to T0PS macro s
        endm


setTMR0 macro
        movlw    _T0CON
        movwf    T0CON
        endm

setTimer0
        ; preparing Timer0 settings
        TMR0(ON)
        T0PS(.256)
        ; make the settings live
        setTMR0

Not sure if that makes things more productive or less error prone - you may
can write extensive macro sets like this which will be MCU independent
however.

Tamas


On Tue, Jul 8, 2008 at 10:18 AM, Xiaofan Chen <xiaofanc@gmail.com> wrote:

> On Tue, Jul 8, 2008 at 2:42 PM, David Meiklejohn <david@gooligum.com.au>
> wrote:
> > Chris wrote:
> >>
> >> You could in principle specify the 0 bits too:
> >>
> >>   movlw (1 << TMR0ON) | (1 << T0PS2) | (0 << T0PS1) | (1 << T0PS0)
> >>
> >> and similarly for the other 0 bits, which I haven't got handy.
> >
> > I prefer to specify individual bits like this, but leave bit fields (such
> > as the three prescaler bits here) in binary, as in:
> >
> >  movlw  1<<TMR0ON | b'101'<<T0PS0   ; turn on TMR0, prescale = 64
> >
> > I do like Olin's method, but otoh, it seems reasonable to expect that
> > someone working on the code will have the data sheet at hand.
>
> I agree that we need to consult the dustsheet. But still I think
> Olin's method is much better and clearer. I understand people
> who are proficient with C like to use "<<" or ">>" but it is
> not as clear in the context of assembly programming.
>
>
> Xiaofan
> --
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http://www.rudonix.com
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