Hallo Arif,

1. You NEED a storage scope! When trouble shooting often situation occurs, that a strange erratic pulse train on a chip pin has to be analyzed. Then, only a storage scope can really help.

2. You NEED at least two channels! When trouble shooting often situation occurs, that you must find out which pulse edge from two or more different signals comes first. This is especially necessary to find out whether setup times or hold times are violated. Then, only a two channel scope can really help.

3. You NEED a scope, which is fast enough! But what is 'fast enough' depends on your needs:
Assume you have a standard 89C52 micro running at 11MHz clock frequency. If you now only want to have a look at /RD or /WR signal line to find out, whether there's a signal at all, then even a 10MHz is enough. Why?
A 10MHz scope has a rise time of about 35nsec, which depends of course on actual brand. With standard 89C52 microcontroller /RD pulse width is specified to be (6 x tclcl -100)nsec minimum, which is about 450nsec. So, 35nsec rise time is 8% of signal width, which means, that the existence /RD pulse can clearly be seen.

But: The real interesting issue is not only to find out whether there's /RD signal or not, but to find out how the /RD pulse looks like in detail, e.g.: Are the edges fast enough, is there some ringing, how much does capacitive loading degrade signal integrity, how much Vcc ripple exists, is the choosen decoupling capacitor adequate, what about ground noise between chip 1 and chip 2, was the stripline designed properly, or are reflections present???????

All these questions can only be answered, if your scope is at least three times faster than the fastest signal your microcontroller can develop: Assume your micro delivers signals containing edges with rise time of about 5nsec, then your scope must have a rise time of at least about 2nsec! So, if you are interested to really analyze fine structure of microcntroller's signals, then even a 100MHz scope might not be fast enough.
It depends on you, what you expect to see with your scope! In most situations (but not all!) with standard 12-clock 89C52 microcontrollers 100MHz storage scope with two channels is very helpful!

Many people have the eroneous idea, that with a bit experience and some reading between the lines the natural limitation of bandwidth can be extended by the help of 'physical intuition'. But just here the most mistakes and misinterpretations take place!! So, whenever you have a serious problem, which cannot be solved by a 100MHz scope and which looks very very suspicious, go to a friend which has a faster one...

By the way: It's not always wise to choose the fastest scope for a measuring session! With 1GHz scope so much noise and interference can be superimposed to signal, that signal can be totally buried in noise! In such situations it's not easy at all, to find out what is actual signal and what is stray-coupling from outerworld, having nothing to do we the application. Working with a really fast scope can be a 'science' sometimes...

Kai