Surviving 1 second without battery power

[skimask]

Maybe Im missing something from your answer <scratching head>

Ok, I smell what your cooking...
Put a meter on the cap and see what it reads and how fast it decays.
Maybe it's a version of a super-cap in a really small package.
PIC's (nano-watt PIC in particular) can draw some seriously LOW current in a sleep mode.

[peu]

I think I understand what you guys mean, this would be the metacode

set BODEN config bit to 1

set BOD bit to 1
set POR bit to 1
read level from eeprom / set level

mainloop
check for BOD/POR bits at PCON register
if BOD=0 then wait for POR=0 and change to next level and write it to eeprom.
goto mainloop
end

Is this correct?

I have some questions:

What would happen if power is lost while writing to eeprom?
Can this be handled with PBP without using interrupts?

Regarding the cap, I don't have a oscilloscope to see the discharge curve, it seems to last around 1seg to fall below 2v but this measurement was done by the eyemeter.

[Acetronics2]

Hi, Peu

NO, you did not understand ...

1) You enable BODEN, nothing else required ...

2) AT program start, you first read the BOR bit

3) If BOR Bit = 0 THEN (and only IF ) you increase the EEPROM content : That means power is back, and did not reach ZERO !!! ( no Pb to write , then ...)

4) If BOR Bit = 1 power has gone to ZERO ( and BOR bit has been reset ) ... just read the EEPROM content .

5) you SET BOR bit

6) you run your "lighting" program ...

Think simple !!!

Alain

[peu]

KISS principle... I know... Im getting older&rusty (just crossed the 40 mark).

Will give your post explanation a try in real code and let you know. Thanks!

[peu]

Hi, Peu

NO, you did not understand ...

1) You enable BODEN, nothing else required ...

2) AT program start, you first read the BOR bit

3) If BOR Bit = 1 THEN (and only IF ) you increase the EEPROM content : That means power is back, and did not reach ZERO !!! ( no Pb to write , then ...)

4) If BOR Bit = 0 power has gone to ZERO ( and BOR bit has been cleared ) ... just read the EEPROM content .

5) you run your "lighting" program ...

Think simple !!!

Alain

Im kinda lost again:

From TABLE 9-6: INITIALIZATION CONDITION FOR SPECIAL REGISTERS
PCON is initialized with %00000010 (POR=1 BOD=0)

From 2.2.2.6 PCON Register
REGISTER 2-6: PCON — POWER CONTROL REGISTER (ADDRESS: 8Eh)

bit 0 BOD: Brown-out Detect STATUS bit
1 = No Brown-out Detect occurred
0 = A Brown-out Detect occurred (must be set in software after a Brown-out Detect occurs)

From these datasheet entries I dont understand when BOD goes to 1

[Acetronics2]

Hi,

Do not worry !!!

1 = No Brown-out Detect occurred
0 = A Brown-out Detect occurred (must be set in software after a Brown-out Detect occurs)

sooo ... just use the Bit level corresponding to what happend ! ... invert BOR levels I indicated for 3) and 4) and you'll have it ...

I've correct the thread , NOW ... I had not used that feature for a while ...

<< Im getting older&rusty (just crossed the 40 mark). >>

... and me the 51 Mark !!!

Alain

[peu]

Hi, Peu

NO, you did not understand ...

1) You enable BODEN, nothing else required ...

2) AT program start, you first read the BOR bit

3) If BOR Bit = 0 THEN (and only IF ) you increase the EEPROM content : That means power is back, and did not reach ZERO !!! ( no Pb to write , then ...)

4) If BOR Bit = 1 power has gone to ZERO ( and BOR bit has been reset ) ... just read the EEPROM content .

5) you SET BOR bit

6) you run your "lighting" program ...

Think simple !!!

Alain

I still have a doubt: when does the BOD bit goes from the initialization value ZERO (table 9-6) to ONE (No Brown-out Detect occurred) in a cold start scenario?

At cold start the circuit should read the stored eeprom value not write a new one

[peu]

Im reading different PIC datasheets so shed some light about the BOD sequence, but most of them share the same wording, Im really lost.

I made a little proggie to test what I've learned in this thread, but it does not work, maybe Im missing something stupid, but after many hours of trying, maybe what I need is a good rest:

@ device pic12f683,INTRC_OSC_NOCLKOUT , wdt_on, mclr_off, protect_off, bod_on

CMCON0 = %00000111     ' Disable comparator
VRCON  = %00000000     ' disable


'       I/Os
TRISIO = %00000000      ' no inputs      

' definitions
           
BODD var PCON.0

gpio=%00000100            'I know program cold started
pause 1000                'gpio.2 green led pin5 indicates coldstart
gpio=%00000000   

loop:

if BODD=0 then           
    gpio=%00000010        'GPIO.1 red led PIN6 shows a BOD state
    pause 1000
    gpio=%00000000
    BODD=1
endif
goto loop

then the schematic is pretty simple, a ceramic capacitor at the power lines for storing some battery, a couple of leds at the specified pins and a momentary switch that allows me to cut VDD for a moment.

It does not vork

[edit] Maybe I need to check for POR=1 and BOD=0 to know for sure that a BOD reset happened

Help!

[Acetronics2]

gpio=%00000010 'GPIO.1 red led PIN6 shows a BOD state
pause 1000


Here is the best reason ( may be others ... I must check ) for your gadget not to work ...

THE DEVICE MUST DRAW AS LITTLE CURRENT AS POSSIBLE !!!

Your led leads VCC voltage to ZERO ... so ... POR and not BOR !!!

Alain

[peu]

Rest helped clear my mind

I will test this code as soon I arrive at my office:

@ device pic12f683,INTRC_OSC_NOCLKOUT , wdt_on, mclr_off, protect_off, bod_on

CMCON0 = %00000111     ' Disable comparator
VRCON  = %00000000     ' disable


'       I/Os
TRISIO = %00000000      ' no inputs      

' definitions
 
' init values

if PCON.0=0 then
  gpio=%00000100            'Brown-out detected turn on LED on PIN5
else
  gpio=%00000010            'Brown-out NOT detected turn on LED on PIN6
endif

'main loop

loop:
goto loop

I can't imagine simpler code to test the BOD function. Do you see something wrong?