My PIC can't do the math! Can yours?

[sayzer]

Is it too early to call this a bug? Or the bug is in my head?

Attached is an excel file (file extension needs to be changed to xls).

There is a match-table in the file. The red cells are incorrect math results from PIC. All other values provide the correct math result.

(16F877 with PBP2.46)

- All variables are word size.
- 20Mhz OSC and 10-bit ADC res.

'
'This is only the loop part.
'

Loop:

ADCIN 1,TempRead
IF tempread>51200 THEN tempread=51200 'Min. temp.
IF tempread<41600 THEN tempread=41600 'Max. temp.


XF=( TempRead /64)-650	       'This is the formula with 1 unit increments.

XB=303		               'This is the initial matching Temp value.
FOR XA=0 to 150	               
   XB=XB-2		       'Each 64 unit increment/decrement is 2˚C
   if XF =XA then XF =XB       'We get the actual temp in Celsius.
next XA

Lcdout $fe,1,”Temp:”, #XF


GoTo loop

For example, if the TempRead value is 44864, then I get the XF as 199 which is correct.

However, if the TemRead value is 46464 then I get XF as 3 which is incorrect. I should be getting 149.

From 46464 to 48000 all results are incorrect. Remaining values are correct.


Should we call this a bug, I am not sure.


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