Powering and reset PIC16LF88 problem

[harryweb]

HI,

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

   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 ?

[Charlie]

Note this diagram does not actually show power connections to the PIC.
This looks unnecessarily complex, and it appears the PIC can choose it's own power for some reason. If you want to power a PIC from either of 2 sources, why not simply throw out this entire circuit except for D3/D4 with the anode of D3 connected to WAY1 and the anode of D4 to WAY4? (Common Cathode to VDD).

[harryweb]

Hi Charlie,
Note this diagram does not actually show power connections to the PIC.
Yes it is because of the ISIS software (hiden powering rails). But power connection is from D1+D2 (common cathode)
(D3+D4 is used for powering RF and control circuit: not on this shematic)

Cannot change this... PCB's already made !

Regards

[Charlie]

What supply voltages are you using? (And if the answer is 5V, remove the zener diodes and try again to see if it works.)