Hey!  I can finally contribute!

From the datasheet (I am looking at the sheet for the 18f242 that I just
finished the same type of project for):

<quote>
NOTE:  TXIF is not cleared immediately upon loading data into the transmit
buffer TXREG.  The flag bit becomes valid in the second instruction cycle
following the load instruction.
</quote>

therefore, your test at a1, which is the first instruction following the
load, is testing TXIF before it gets updated from loading TXREG.


Hope this helps!

--Joe Jansen




pic microcontroller discussion list <PICLIST@MITVMA.MIT.EDU> wrote on
03/05/2004 08:46:19 AM:

> >> I'm experiencing strange behaviour with the 452 and the PLL enabled:
>
> >You do know that the PLL on/off setting takes its (new) effect only
> after a power down - power up?
>
> Yes I do, I found out the hard way the first time I tried to use it :-)
>
> Each time I enable or disable the PLL I remove power and then reaply...
>
> Also I discovered another problem I can't figure out. The following
code:
>
>   movlw 'T'
>   movwf TXREG
> a1:  btfss PIR1, TXIF
>   goto a1
>   movlw 'e'
>   movwf TXREG
> b1:  btfss PIR1, TXIF
>   goto b1
>   movlw 's'
>   movwf TXREG
> c1:  btfss PIR1, TXIF
>   goto c1
>   movlw 't'
>   movwf TXREG
> d1:  btfss PIR1, TXIF
>   goto d1
>   movlw '-'
>   movwf TXREG
> e1:  btfss PIR1, TXIF
>   goto e1
>
> That should give "Test-" as a UART output gives only "Ts-"! Baud
> rate is 19.2Kbps. Even if I put it at a continous loop it keeps
> displaying "Ts-Ts-Ts-Ts-". The same code with a 877 in place of the
> 452 works fine.
>
> Could it be that my micro is damaged? How could that happen?
>
> John Spiliotopoulos/Greece
>
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