Powering and reset PIC16LF88 problem

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 ?


Attachment 6367

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).

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

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