>>If you want to save on the component count, there
>>are no reasons to BOTH have a pull-up AND a series
>>resistor for the base of the transistor.
>>Simply put one resistor from base to VCC that will
>>ensure proper operation of the transistor. Then
>>connect the open drain output to base.
>>When the output is driven low, the current through
>>your resistor will go directly to ground. The base
>>voltage will be well below 500mV, and no ib and ic
>>will flow.

>But this will not work if other pins on the same
>port have to be set / cleared whilst preserving the
>value of the RA4 pin, because if you write a 1
>to RA4 in this case, the voltage on the pin will be
>0.6V and read in as a logic 0.

If you "shadowed" PORTA and moved this shadow register
into PORTA when you needed to change a pin, wouldn't
his suggestion work?


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