PIC 16F819 Turn-On Problem

[Dick Ivers]

Hi,
Thanks for your replies.
My circuit is supplied from a battery driven voltage regulator which is fully on before the power is switched to the circuit.
I neglected to mention that there are actually 2 solenoids and 2 mosfets. It is only the second one that misbehaves. Yes, I have 2 initialization steps at the very top of the code...already thought of that:

low portb.3
low porta.1

I don't have a scope. The solenoids are very fast and can operate in less than 100 us. I will try the cap idea from Melanie. Otherwise, will go to a p-channel mosfet on my next board.

Dick

[Bruce]

If you have a device that can react that fast to a power-on condition, you
might also consider disabling PWRT (power-up timer).

PWRT alone can introduce a power-up delay period of roughly 72mS before
any code can execute & set/clear outputs. Factor that in with normal start-
up times, and you can end up with a substantial delay period before you can
initialize everything properly.

I think the PBP config word defaults in most device header files have PWRT
enabled, but if your power supply comes up quickly, and you don't see erratic
behavior on power-up with PWRT disabled, that just might cure the problem.

[Dick Ivers]

Bruce,
PWRT is already disabled. Here is the whole configuration line:

@device pic16f819,intrc_osc_noclkout,wdt_on,pwrt_off,mclr_ off,bod_off,lvp_off,cpd_off

@ device ccpmx_off,debug_off,wrt_off,protect_off

I will try M's cap fix. The approach makes sense because it creates a transient path to gnd for the spurious voltage. Can't do this right away though...will have to wait.

Dick

[markedwards]

Dick,

Did you ever solve your 16F819 Turn-On problem?

Like Bruce recommended, I have found the PWRT seems to help.
I am also using INTRC and initialize to OSCcon = $60 (4mhz) and
later switch to OSCcon = $70 (8mhz) at the end of my initialization,
just before my main loop.
I have used 16F627A with INTRC, and 16F876, 16F872 w/ crystal and never had power up Turn-On problem like the 16F819.

Mark

[peterdeco1]

Hi Dick. I had exactly the same problem with a 16LF818 attached to a music chip. Upon power-up the chip would blast a few milliseconds of music from the speaker. I cured the problem by turning "POWER UP TIMER OFF". It's been about a year now and no problems have arised by doing this.

[Dick Ivers]

Peter and Mark,

No, I never really solved the problem, and yes, the power-on timer is already set to off as explained earlier. I have now moved past the problem because I no longer use the super-fast solenoid. Have gone to a servo instead .. no problem.