HI,

I'm working on a GPS project. The pic16lf88 may be powered from 1 or/and 2 sources (GPS)

Code:
   OSCCON =100000

   TRISA =010000
   TRISB =000101
   
   ANSEL =010000      'an4 analog not used at this time
   
   PORTA = 0
   PORTB = 0
   
   clear
   
   led    var     porta.0
   way1   var     portb.0
   way4   var     portb.2
   X      VAR     WORD


   pause 10
   HIGH PORTA.3    ' powering antenna
   
   mainloop:
   
   X = X + 1

   IF X = 10000 then
   toggle PORTA.0  'led
   X = 0
   endif
  
   
   IF way1 = 1 and way4 = 1 then
   low PORTB.4
   HIGH PORTB.7
   goto mainloop
   endif
   
   if way4 = 1 then 
   PORTB.4 = 1
   PORTB.7 = 0
   endif
   
   if way1 = 1 then
   PORTB.7 = 1
   PORTB.4 = 0
   endif

   goto mainloop

When my pic is powered from
way1 = ok
way2 = ok
way1 + way2 = ok
way1 + way2, then cutting power from way2 = ok
way1 + way2, then cutting power from way1 = NOT OK PORTA.3 (antenna) becomes LOW !!!
I have tried to play with BOREN without success. When enabled the circuit doesn't work at all.

Simulation works great with ISIS, not with real circuit.

Can someone help ?


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