Hi Jan-Erik,

I do not know, at the moment I have not access to 4450 but at least on
simulator (MPLAB 7.41) if I put in the order Jinx did TMR0H does not get
transferred into the TMR0 register tough I see it in the special
funct.regwindow like it was - I got something 6ms delay in this way,
but with the
order the datasheet describes I got the 104ns timings.

Tamas


On 6/27/07, Jan-Erik Soderholm <jan-erik.soderholm@telia.com> wrote:
>
> That is correct, but in this case (as I understod it)
> TMR0L is never *read* and TMR0H is never written with
> anything else then 0xFC, so the TMR0H-buffer whould have
> the correct value anyway. But, I'd write them in
> the correct order anyway...
>
> Jan-Erik.
>
> Tamas Rudnai wrote:
> > Hi Jinx,
> >
> > I think you have to write TMR0H first which is a latency byte only and
> it
> > updated when you write TMR0L. Reading is the opposite way, TMR0H updated
> > when you read TMR0L.
> >
> > Regards,
> > Tamas
> >
> >
> > On 6/27/07, Jinx <joecolquitt@clear.net.nz> wrote:
> >> I've spent way too much time on this today trying to figure out
> >> what's going on. Maybe someone can see something I can't
> >>
> >> Code for a s/w UART on an 18F4550 should have been straight-
> >> forward, but TMR0 isn't doing what I expected
> >>
> >> Fosc is derived from a 3.2768MHz crystal, and instruction cycles
> >> are being measured as 101.72ns, so the PIC is running at 39.3216
> >>
> >> The loading I have for TMR0 should make about 104us, which
> >> is the bit time for an 8MHz 18F1320 set to receive 9615 baud
> >> (eventually the 4550 will be bumped up to 48MHz for USB and
> >> the s/w UART will also be transmitting at 9615 baud)
> >>
> >> I calculate
> >>
> >> $10000 - $0FC02 = $003FE = 1022, * 0.10172 = 104us
> >>
> >> But TMR0 puts out 757.85us. I can't figure out what needs to
> >> be done. It's not a recognisable multiple (~ 7.28), so counted
> >> out a pre-scaler. The msdelay does put out the calculated 1ms,
> >> so Fosc is good
> >>
> >> No interrupts or WDT enabled. The h/w UART is comming
> >> with an external device at 9600 baud, no problems
> >>
> >> Any ideas ? Please ?
> >>
> >> TMR0 set-up
> >>
> >>          mov     b'000001000',t0con
> >> ;                  0          t0 off
> >> ;                   0         16-bit
> >> ;                    0        internal clock
> >> ;                     x
> >> ;                      1      no pre-scaler
> >> ;                       xxx
> >>
> >> Test transmission
> >>
> >> txa5     movlw   0x55
> >>          call    txw
> >>          call    msdelay
> >>          movlw   0xaa
> >>          call    txw
> >>          call    msdelay
> >>          bra     txa5
> >>
> >> ;================================================
> >> ;        Transmit byte from W - set dtx high/low (inverted)
> >> ;================================================
> >>
> >> txw      movff    wreg,temp
> >>          mov      8,cnt0
> >>          bcf      dtx          ;Start bit
> >>          call     bitdel
> >>
> >> byte_out btfss    temp,0
> >>          bra      zerobit
> >> onebit   bcf      dtx
> >>          call     bitdel
> >>          bra      nextbit
> >> zerobit  bsf      dtx
> >>          call     bitdel
> >>
> >> nextbit  rrncf    temp
> >>          decfsz   cnt0
> >>          bra      byte_out
> >>
> >>          bsf      dtx          ;Stop bit
> >>          call     bitdel
> >>          return
> >>
> >> ; 1 bit delay, 104.004us
> >>
> >> bitdel   mov      0x02,tmr0l
> >>          mov      0xfc,tmr0h
> >>          bcf      intcon,tmr0if
> >>          bsf      t0con,tmr0on ;timer on
> >>          btfss    intcon,t0if  ;wait for rollover
> >>          bra      $-2
> >>          bcf      t0con,tmr0on ;timer off
> >>          return
> >>
> >> --
> >> http://www.piclist.com PIC/SX FAQ & list archive
> >> View/change your membership options at
> >> http://mailman.mit.edu/mailman/listinfo/piclist
> >>
>
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist