Logic Analyzer Recommendations

[Joe R.]

At 12:48 AM 10/18/05 +0100, you wrote:
>> 
>> For those of us who are semi electronically inept (i.e. can replace
>> components and burn eeproms, but not much else) what is a logic analyzer,
>> what is it used for, and what situatios would require tyou to have one? (or
>> when would it be helpful?)
>
>A logic analyser is basically an oscilloscope for digital signals.
>
>They have a number of input chanels (anything from 3 to over 100) that 
>you connect to various points of the device under test. The logic state 
>of all those points is recorded every so often (say every 50 ns), the 
>time being selectable of course.

  Or the sample time can be based on other signals such as the phase of a
clock signal. That's REAL useful for picking data or address off of a
multiplexed bus.  Many LAs also have a feature to look for and display
glitches (fast narrow pulses that shouldn't be there) on the signal lines.
That can be a real life saver as well.

   Joe



 You can then display those recorded 
>states as a timing diagram, and sometimes as a table of values (you 
>'tell' the analyser that channels 0-15 are to be displayed as a 4 digit 
>hex number, that channels 16 to 23 as a 2 digit hex number, etc). Some 
>analysers even let you load a disassembler program for a particular 
>processor at which point you can display the result as a dissassembly 
>listing [1]
>
>You can set the analyser to trigger on a particular combination of inputs 
>(that's the simplest case, many analysers have very complex trigger 
>modes) and then either start recording when you get the trigger, stop 
>recording when you get the trigger, or carry one recording for about half 
>the analysers memory size on the trigger (so the trigger event occurs 
>aproximately in the middle of the data that's been recorded).
>
>As to why you'd want one, well, if you have a complex digital circuit, 
>and you need to see what's going on (either because you've just designed 
>it and need to find out what mistake you've made this time, or because 
>it's stopped working), a logic analyser will let you look at all the 
>signals in said circuit at once and display the relationship between 
>them.
>
>[1] Personally, I think this is a somewhat useless feature. Of much more 
>use is the ability to link the analyser to a computer (e.g. via GPIB, 
>RS232 or these days I guess USB) and transfer the recorded data. Then you 
>can attack it with any program you like.
>
>-tony
>