The only way to make your LED shine with the PNP Darlington BDX54C is to connect the emitter to +5V:




As shown in the datasheet http://www.datasheetcatalog.org/datasheet/mospec/BDX54.pdf the BDX54C contains internal resistors across base and emitter(s) which can serve as pull-up in the case that Px,y is a Port0 line.

Take care, when continuously driving a standard LED a current limiting resistor of 15 Ohm, as mentioned in one of your previous posts, is way to small! 150 Ohm, which I have drawn in the schematic is definitely a better choice then. 15 Ohm makes only sense in a multiplexed system, or when your LED is only turned-on during a small period of time (in the range of 100µsec in conjunction with a duty cycle of 10%, which depends on LED of course).

So, before you actually put this 15 Ohm into your circuit, first make sure that the code of micro is running properly, only driving the LED during a small period of time.

You will notice, that the LED goes on, when Px,y is emitting low state. This makes sense, because during power-on reset all the pins are emitting high state for the duration of reset time, which could change your board into a barbecue otherwise.

Don't forget to provide proper power supply decoupling at the emitter of BDX54C! Put 100nF X7R ceramic in parallel to 47µF electrolytic from the emitter to the ground terminal of 15/150 Ohm resistor, with shortest leads!!

Kai