On Mon, 29 Sep 1997 13:56:30 -0500 Shabbir A Bashar <s.bashar
spam_OUTKCL.AC.UK>
writes:
>-- [ From: Shabbir A Bashar * EMC.Ver #2.5.02 ] --
>
>Hi all,
>
>I am more into electronics than programming but I'm just starting on
>the PIC 16c84.
>
>However, I get nothing (other than the correct voltages at drain and
>source ports).
>
>Using my nasty (ancient) oscilloscope I can not detect any
>oscillations coming from either clock pin. One of the clock pins is
>at 0V and the other sits at roughly 0.24V.
Measuring with a high-impedance device like a scope or digital voltmeter,
you should have about 2.5V at both oscillator pins, whether the
oscillator is running or not. About the only thing that can change this
is executing a SLEEP instruction or setting the oscillator fuses to the
RC type. Looking for oscillations with a scope is not a reliable test
since the loading of the scope may make the oscillator start or stop.
But the DC voltage should set itself to half-supply.
I've seen a PIC16F84 do strange things when the power comes up slowly (as
can happen if the input of your 5V regulator is driven from a small
transformer with a large filter capacitor). The oscillator refusing to
work was not one of those strange things but it could happen.
>
>The XTal fuse was set when I programmed the pic.
Put the PIC back in the programmer and read it, make sure the fuse is
actually set that way. Be sure to disable the WDT. Leaving it on will
cause the PIC to reset itself periodically. Try to pull one of the pins
that should be output to +5 and ground with a resistor, if the voltage
does follow then the tri-state register hasn't been set. This could be
because the program isn't running at all, or it could be improper
software. All the pins change to input mode when the chip is reset.
{Quote hidden}
