How long does it take for an 8 bit PIC to stabilize after Power-up?

[Art]

Last edited by towlerg; Today at 00:38. Reason: old and stupid

That’s a bit rough!

It will loose time with temperature, and any supply voltage fluctuation (batteries).
It’s ultra cheap, you can use serial, but not keep or measure time with it.

[Art]

That’s an interesting find.
You could probably cycle the calibration value at run time then.

for value = mincalvalue to maxcalvalue
calvalue = value
turn led on
pause
turn led off
pause
next value

You could probably calibrate it yourself with a good freq counter,
and double check their work or what they thought was operating temperature.

[Demon]

Does anyone have an answer to the original question?

How long does it take for an 8 bit PIC to stabilize after Power-up?

I'm trying to clean up code and wondering just how much we should pause at program start. I have code with pauses of all sorts of lengths.

How about:
- without LCD
- with standard 4x20 LCD

16F18877, also an 8-bit PIC.

[richard]

How about:
- without LCD
- with standard 4x20 LCD

a pic is ready as soon as its osc is stable; as discoverable from the oscstat reg, a handful of microseconds at worst
a LCD can take 100's of milliseconds, 500 not uncommon. its not the same across version/model/maker either
its usually pretty obvious when you have tried to talk to a LCD before its listening

i feel you have the cart before the horse

[Ioannis]

Up to this moment I did not had any special needs for a fast power up, so the 1 sec pause worked just fine for me.

But I am pretty sure that each osc will have its own time to stabilise. So, for 18877, page 112 of the datasheet, says that there is a timer named OST (Oscillator Startup Timer) that counts 1024 cycles of from OSC1, if the Oscillator is set to LP, XT or HS (all these are external oscillators).

For any case of oscillator selection (internal or external), there is OSCSTAT register that displays the status of that module in the appropriate bits (page 122).

Page 603 shows the wake up time that any osc selection needs.

Other PIC have same data also, so you may look accordingly.

Ioannis

[Demon]

...Page 603 shows the wake up time that any osc selection needs...

HFINTOSC is typically 11usec to 20usec max (I don't sleep the PIC)

So PAUSE 1 should be more than sufficient for a PIC without LCDs...?

(I wouldn't bother with PAUSEUS if I don't have to).


Using:

#CONFIG
    __config _CONFIG1, _FEXTOSC_OFF & _RSTOSC_HFINT32 & _CLKOUTEN_OFF & _CSWEN_OFF & _FCMEN_ON
    __config _CONFIG2, _MCLRE_ON & _PWRTE_OFF & _LPBOREN_OFF & _BOREN_ON & _BORV_LO & _ZCD_OFF & _PPS1WAY_OFF & _STVREN_ON & _DEBUG_OFF
    __config _CONFIG3, _WDTCPS_WDTCPS_11 & _WDTE_OFF & _WDTCWS_WDTCWS_7 & _WDTCCS_LFINTOSC
    __config _CONFIG4, _WRT_OFF & _SCANE_available & _LVP_OFF
    __config _CONFIG5, _CP_OFF & _CPD_OFF
#ENDCONFIG

[Ioannis]

If you do not have any LCDs or other peripherals that need time to settle, I am sure that you do not need any delay in your program. If the program reached the first command then the PIC just woke up!

The problem is with other circuits connected to the PIC and are still under Reset period. PIC will not be able to communicate with this only device.

Ioannis

[Demon]

Yeah, hadn't put any thought into MCP23017 requirements.

Gonna have to look at those datasheets.