Hi,

I am

- using a DS89C420
- trying to turn an LED on and off via P1.0
- using a "typical" transistor based circuit I see everywhere as a buffer between the LED and the outport.

Everything works in the sense that the voltage at the pin changes when I set and clear it, and the led changes brightness. However, setting the output pin to 0 does not fully bring the pin 0, but instead a little above, so the LED is always on a little bit which I don't want.

It is typicall around 0.6 - 0.7V above ground when the output bit is set to zero. From what I have read, this about right for between the base and the emitter of the transitor, but if that is true, how to I force a true off condition?

I've tried a few variations, but the current version is"

output pin -> resistor -> base

emitter -> ground

+5 -> LED -> resistor 2 -> collector

Thanks