Maria wrote:

I know that the circuit was used before and worked...

Maria,

please don't feel offended. But as many people here told you, there's something wrong with at least your LED driver circuit. And only the fact, that it worked earlier, does not mean, that it's designed properly!

But although Michael has given you worked-out examples, how to connect your stuff to microcontroller, you still insist that your circuit is working. Why are you doing this?

Last try: Your LED driver circuit is a misconstruction!

I highly recommend you to have a look at the '80C51 family hardware description', which you will find here:

http://www.semiconductors.philips.com/acrobat/v...WARE_1.pdf

Have a look at figure 4, 5 and the according text. This, in combination with your datasheet (!), will explain how the ports are working.

Your LED driver circuit suffers from turning-off of pFET3, caused by your wrong driver circuitry:
When Port pin shall emit high level, first pFET2 and pFET3 are turned-on. But caused by your unsuited driver circuit, voltage at Port pin breaks down. If voltage sinks below about 2.0V (depends on derivative), pFET3 is turned-off and only very weak pull-pup pFET2 is turned-on. But this can only deliver about 10...20µA, so that your LED is shining only very dim.
Unfortunately, your base resistor is choosen so unsuited, that voltage at Port pin is exact at threshold voltage of this mechanism! At voltages slightly higher than threshold voltage, Port pin can deliver up to 500...650µA maximum (depends on derivative). This current causes a voltage drop across 2k2 resistor of about 1.1...1.43V. Adding base emitter voltage of about 0.7V gives totally 1.8...2.13V. So, with a bit luck, voltage at Port pin is higher than threshold voltage (about 2.0V), then Port pin can deliver high base current of about 500...600µA and your LED is shining bright. But if threshold voltage or output current are changing only sligthly for some reason and voltage at Port pin falls below threshold voltage, then your LED is only shining very dim. This can happen all the time and has nothing to do with your software!

So, please change your LED driver circuit!

It would be the best to use PNP transistor driver. Michael has drawn some very nice schematics here. Please use them!
Please keep in mind, that with PNP transistor LED will be turned-on, when Port pin is emitting low level!

By the way: I did not understand your buzzer driver. May be you should change this design, too.

Kai