I'm Sorry!!! I'm wrote wrong about RB4 Pin!!
Mark Willis email (remove spam text)
Alice Campbell wrote:
> another thing to try before complete panic:
> 1.using voltmeter, measure voltage from vss to vcc. is it 5v? if
> not, fix it, and go to step 2.
> 2. measure voltage from -mclr to ground. is it 0? if not, fix it,
> and go to step 3.
Um... Um... Uh... <Cough Cough>
I usually pull ~MClr UP to Vss/Vcc (+5V), through a 10k resistor (for
example), if it's at Ground the PIC's being held in reset, don't expect
the PIC to run...
> 3. measure voltage on osc1 and osc2. they should be somewhere
> between 1.5 and 3 volts. they are generally a little different, but
> both pins ought to have some voltage. if not, it isnt oscillating,
> probably. fiddle with capacitor sizes. try doubling up on the 15
> pfs for a total of 30pf on each leg.
... Except your O-Scope or DVM probe may well affect the operation of
the oscillator drastically, best/easiest to use a buffer & check that
the buffer's output has a nice clean wave on it - or use a 10x O-Scope
probe, and expect some frequency deviation if your circuit's running
And there's the ever-popular RA4 problem where people forget that RA4
is open drain (i.e. will only ground itself, not pull itself high), but
this isn't applicable here as you're talking RB4 not RA4. I mention
this just in case you MEANT RA4 <G> (I've done worse than that,
See also: www.piclist.com/techref/index.htm?key=sorry+wrote+wrong
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