I am pulsing port3 pins (AT89C2051) at 16kHz frequency with 10K pull ups.When I measure output voltage with general digital multimeter (with DC voltage measurement selected) it shows 2.56 volts.I do not have CRO to see the wave forms.Is the reading of DMM average value of actual voltage or AT89C2051 is able to provide only 2.56 volts.I am expecting the DMM to show 5V.Does the value of Pull up resistor or pulsing frequency affect the output voltage of the port pins