power up problem

[rookieofbasic]

Hi guys!
I have problem with power up my pic project. The problem appears when i power up my pic hardware after leaving if off for a couple of hours. I have to turn it on and off several times in order for it to work.

[Melanie]

I've probably written this several times over the years, but like a car that requires Fuel, Air and Spark, provide those and it's guaranteed to work, a PIC also requires three things, and in the PIC's case it's Power, Clock and Reset. If you have those correct, the your PIC is also guaranteed to run.

From what you write (which is very little and doesn't give us much information on which to base a comment), I'll suspect a power supply with a very slow rise-time at Power-On. If it's a Battery, it's probably weak. If it's from a dedicated Line Power Supply, is it under-rated for the current you are drawing from it? If it's a weak PSU and if you have large smoothing Capacitors then that could also be a reason.

Melanie

[rookieofbasic]

Thanx alot Mel, I use the battery to power up the circuit. It may be just does not provide enough current at first couple attempts. But this design suppose to be a portable unit, so i can't connect it straight to the 5V power supply. I also use to 4mhz crystal. I got the keypad and the lcd to work, also have the data to save into the memory bank. I am trying to send the data which i saved in the bank to the Serial out, by using TXREG. I tried a couple of different methods of serial out("serout, baudrate,[]", and "POKE TXREG") without any success. Do you have any suggestion?

[Melanie]

Just temporarily as a test, put a 220uF (or similar) directly across the Battery and THEN switch the PIC circuit On/Off from that Battery/Cap combination. The Capacitor may well be able to provide a reservoir to overcome the initial current draw which is probably causing a lazy PSU startup. If this works, you can easily construct a pre-charge circuit to charge a capacitor at switch-on and thereafter turn the PIC on a second or so later.

[Kypros]

Hi,
as Melanie said, you may have a weak power supply.
On the other hand, it is a good idea to check u r reset circuitry whether it brings the MCLR pin to logic high. Check this at the moment u r circuit does not start. Also at this moment, try to trace your clock. Does your crystal oscillates?

Perhaps a capacitor on the RESET network (if you use one) has leakage current to ground. Just an assumption.

Anyway, I always enjoy and read the answers given by Melanie
Regards
Kypros