Anand Gadiyar wrote:
> Using a voltmeter, the Vcc pin shows 5 volts with respect to GND.
> And a output pin at logic high shows 4 volts with respect to GND. The
> same pin shows 0 volts with respect to the Vcc pin. The same is
> observed when i used a CRO to look at the waveforms.

This is consistent with the pin having a high impedence connection to Vcc.
The surprising part is that a voltmeter and oscilloscope would read the same
value, but maybe you were using a 10x probe with the scope.  10Mohms is then
believable for both.  If so, the connection to Vcc looks like 2.5Mohms at
that voltage.  Since that's a unlikely deliberate value, it was most likely
a floating input with leakage from Vcc.  The total leakage out of the pin
was 400nA at 4V.  That sounds a little high for most cases of CMOS inputs,
but is still within the data sheet limits of many devices, especially at
elevated temperatures.  Non-CMOS inputs can easily require this much bias
current, which I guess is the case since you said Vcc instead of Vdd.


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