http://www.semiconductors.philips.com/acrobat/v...UIDE_1.pdf
Will tell you how many cycles the various instructions use. A cycle will be 1,4,6 or 12 clock times depending on your derivative.

A much simpler method is to wrap the routine in a loop that executes your snippet 10.000, 100.000 or even 1.000.000 times and changes the state of a LED on each expiration. Then use a stopwatch. This way a 500 uS loop will go for 500 seconds - stopwatch and observation should be precvise enough.

Your questions such as: "Q1. Value of R0 when 200 micro seconds have lapsed ??? " indicates that you intend to test r0, this will dramatically change your loop time.

A much better approach than "testing R0" would be to call the timing loop with r0 preloaded with a value rather than always loading zero.

Have fun,

Erik