piclist 1995\11\06\053433a >
Thread: problem with circuit startup
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face BY : Conny Andersson email (remove spam text)



At 16.57 1995-11-05 +0000, Walter Andersson wrote:

>I've put together a simple circuit board for use in prototyping PIC
>projects.  The board is constructed using wire wrapping techniques.
>I've hooked the proto board up to a simple breadboard circuit
>consisting of LEDs and resitors connected to each of the ports on
>port A & B.

I hope you don't overload your PIC with all these LED:s. Normally each
LED should get 10-20mA and 10 of them should have up to 200mA, way too
much for our little friend. For the PIC16C5X series the absolute maximum
rating is 150mA out of the VSS pin and max 50mA in to VDD pin. Max output
sunk by a single I/O port is 50mA and max output current sourced by a
single I/O port is 40mA. Each port pin can take 20mA alone (sourced) and
25mA (sunk). Well, maybe it works anyway but it wont hurt to be on the
legal side ... :)

>MCLR tied to +5v through a 1k resistor, with a pushbutton switch to
>ground to provide a reset switch.  OSC1, OSC2 to a xtal and two caps.
>RA4/RTCC is tied to +5v

Try to add a low pass network and some diodes to your switch. It will help
to debounce and make a slow reset. There are a few good circuits in the
uC-databook.

You might also need a smoothing capacitor say 100nF at each digital IC and
connected between VDD and VSS.

>The problem is the circuit doesn't startup properly.  Using a freq
>cntr I've checked the oscillator and it is runnning.  Turning off the
>power supply to the circuit starts it as the power supply discharges.
>By reapplying power the circuit will continue to function; however,
>when I press the reset button the circuit fails to restart.

Look at your power rails close to the pic via an oscilloscope, It
might help you locate the problem source.

>BTW, the WDT, is off

Aha, that's nice!

-- Conny
<9511061034.AA19773@MIT.EDU>

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