Just some minor tips...

If you'd like more people to read your post, you
realy should make sure that you posts are easy
to read. Line up the code. Don't put instructions
in col 1 (it's not like that i your original code,
is it ?). That part with the FALSE/TRUE/GOTO realy
should have been cleaned up before beeing posted !

It could also help to see all relevant info,
such as the setup code for the ADC in this case.

And writing code using the builtin symbols provided
by the Microship include files helps a lot, such as
writing "btfss   status, C" instead of "btfss   status, 0".
This way, we don't have to open the data sheet to
look up if bit 0 realy is the "C" bit.

Now, even if no one has seen anything yet, you can be more
or less 100% sure that *something* is wrong there.
Cleaning up the code and using symbols, could get you
a fair bit closer to find it.

Jan-Erik.

PS.
Finely, putting the first letter in each sentence in
upper case, makes the text easier to read, and also
shows that you care about those rading it (not saying
that you do *not*, but it never hurts to show it also...)




-----Original Message-----
From: Jeffrey Vitale [mailto:jvitale@CNRIT.TAMU.EDU]
Sent: den 16 oktober 2003 22:13
To: PICLIST@MITVMA.MIT.EDU
Subject: [PIC]: a2d problems with 16f877a


I am able to get an a2d value from my 877 chip reding value from a
potentiometer connected to chip (using chips vdd as vref). after i put the
value's from ADRESH into a user register (via W of course) i perform an
ADDWF where W=D'55' to see whether or not the A2d value is greater than 200
or not (this is my threshold level i am interested in). the strange thing is
that the STATUS carry bit (bit 0) does not stay at 1 like it should when the
user register is 201 and greater. using leds, i am able to verify that the
status bit will only show a MSB carry when the user register is of the
following values:
201 through 207
217 through 231
247 through 255

in the other values the carry bit is 0 as verifed by leds. the pattern seems
to be that the status bit will only show a carry when the lower byte of the
user register being added to W is between 9 and 15, which coincides with a
lower byte carry (STAUS bit 1 D being set).

any thoughts? it is very perplexing.

some of the code:
Main
  call ad_portc
  goto Main

ad_portc
bsf ADCON0,GO ;Start A/D conversion
Wait
  btfsc ADCON0,GO ;  Wait for conversion to complete
  goto Wait

  movf  ADRESH,W       ;Write A/D result to PORTC
  movwf  PORTC ;LEDs
  movwf  Throttle
 movlw D'55'
  addwf  Throttle,W
   btfss   status, 0
FALSE   goto   false_10
TRUE     bsf     PORTB,0
GOTO    continue_10
false_10    bcf   PORTB,0
continue_10
return


thanks,

jeff

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http://www.piclist.com hint: The PICList is archived three different
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http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.

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http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.