Hi:
Old business:
* The page0 - page1 problem is solved in my LCD clock program.  Pushing 
PCLATH in the ISR and popping it at the end fixed it.
*Leap Year can easily be calculated since in order to display the 2 byte 
integer year there is a conversion to 4 BCD digits.  These are easily 
tested for MOD100 and MOD400, so Leap Year is now working.  Also the 
Century for the Zeller Congruence Day of Week is just 10*Throusnds+Hundeds.

New business:
In order to calculate the Zeller Congruence the math needs to be 16 bit 
to handle the 4 digit Year so the Modulo 7 calculation needs to start 
with a two byte unsigned integer and output 0 to 6, but so far it's 
escaped me how to calculate it and there's not even a mention of modulo 
calculations on the piclist.com source code pages.  The start of the 
loop may be something like:

    movlw    7 ; addwf with a -7 does not work
Mod7_Loop
    subwf    Z_DowLo,F  
    btfsc    STATUS,C    ; for subtraction the sense of carry is inverted
    goto Mod7_Loop ; keep subtracting 7 until there's a carry

but the next part has me stumped.  For example in normal math at this 
point Z_DowLo would be negative and if this was a one byte MOD7 just 
adding 7 would bring it to the answer.  So now we need a second loop 
that subtracts one from Z_DowHi and each time that's done makes an 
adjustment to Z_DowLo.  But since this is a MOD7 calculation instead of 
adding 0xFF I tried adding 256MOD7 or 4 for each carry but it does not 
seem to work.  Any ideas?

Thanks,

Brooke Clarke
-- 

w/Java http://www.PRC68.com
w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist