Saving variable(s) contents before power is removed

[ronsimpson]

The PIC16F628 has voltage comparators that can cause an interrupt. In the schematic the programmable reference is compared against a division of the input voltage. If input power falls dangerously low then an interrupt is generated.

I do not see a way of monitoring supply voltage with out using a pin.

Good luck!

[peterdeco1]

Hi Emavil. This is a snippet of code I use with a 16F872 with eeprom. In case of power interruption it will go back to the mode it was in. The line at the top "IF MODE > 2 Then LET MODE = 0" is only valid with a newly programmed PIC. Once a write is performed, it will read a 0 or 1 or 2. Hope this helps.



address VAR WORD 'address variable
TRISA = %00110000
TRISB = %11111101
TRISC = %00000000
Read 1,MODE
IF MODE > 2 Then LET MODE = 0

START:
MAIN PROGRAM HERE


CHANGEMODE:
LET MODE = (MODE + 1) 'ADVANCE MODE
IF MODE > 2 Then LET MODE = 0
Write 1,MODE
GoTo START

[Acetronics2]

The PIC16F628 has voltage comparators that can cause an interrupt. In the schematic the programmable reference is compared against a division of the input voltage. If input power falls dangerously low then an interrupt is generated.

I do not see a way of monitoring supply voltage with out using a pin.

Good luck!

Hi, Ron

Good analysis ...

you can even avoid using a comparator input, as the Schmitt trigger inputs High/Low thresolds of the pic are quite precise ( you can use pin polling instead of interrupts ).
If no comparator available, you also can use a To 92 case MC 33064 P5 or equivalent which will drive its output pin LOW for voltage < 4.65 v.

Alain