Howard McGinnis wrote:
>
> I'm using a 16F873 with the MCLR tied to VCC through a 100K resistor (no
> cap). We've noticed that when we touch the MCLR pin with a Tektronix scope
> probe connected to a floating Tek 465, the processor resets. With a 10K,
> the condition does not appear to occur.
>
> I've looked in the MCHP documentation for recommended configuration of the
> MCLR line with no luck. Any suggestions?
>
> Also, the MCHP docs refer to a Vihh in section 12.18 applied to the MCLR
> pin for the high voltage programming mode, but I can't seem to find Vihh in
> the parameters.


It is Vpp, about 13.0 volts.
Your 100k resistor is a bit large, you can use 56k
or even less and still get good ICSP, if you keep
the ICSP leads under 18 inches long.

Your scope problem is common in TV industry. The
standard solution is to tie the gnd of the scope to
the PIC gnd, then use a 1 meg ohm resistor to connect
to the probe (tip) and connect this to the 5v rail
of the PIC circuit. Then you can measure all the pins
of the chips in circuit without affecting them.

This stops probe drift and the associated spike when
you touch it on the chip. It will also prevent you
from blowing CMOS chips when you touch the probe on
them.:o)
-Roman
PS. You can buy probes with this "bleed" resistance
built in.

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