Detecting an 80-90us Pulse from a 5V Serial Signal

I am trying to detect an 80-90us pulse from a 5v serial signal that also contains faster pulses, its a serial stream of data with the 80-90us pulse being the start of a data block.

I realise this can be done with a Microchip but using such an option gives me further problems later.

Has anyone any ideas or a nice simlpe way to do it.

Basically I want to detect the start which is the signal going low for 80-90us then clock in the serial data using a fixed clock , just this dam start pulse if giving me a huge headache.

Hope you can help

Andy