Hello Mr. Jeff Timo,
To measure pulse width with a standard 8051
all you need is to set up one of your
counters as a standard such as one
millisecond. Wire your input to the below
circuit (frequency doubler) and to interrupt
0 of your 8051. Set it up as a positive
transition interrupt. Put you 8051 into a
loop to start counting the interrupts from
timer one on the rising edge of the input.
When it detects the next rising edge save
the counted value and repeat again to get the
other alternative of your input signal.
http://users.otenet.gr/~athsam/C...4011_a.gif
http://users.otenet.gr/~athsam/C...4011_b.gif


Good luck,
Charles Bannister