Okay, I'm completely new to scopes. I'd like to use a scope to display logic levels from PIC circuits. From what I've read I need 1.5ns risetime  and ~200mhz. Is this correct, or can I get away with less bandwidth??? This is based on TTL levels. I dont really want to spend $1000+ for something, especially if it's overkill. Would a scope of less bandwidth even display TTL logic levels? Should I be looking at a logic analyzer instead??? Would an analogue CRT scope be adequate, or do I need digital? I'd appreciate any input!
Posted on 2006-04-15 11:29:39 by The Dude of Dudes
I would get a scope before getting a logic analyzer. You can see things a logic analyzer won't display, such as jitter, ringing, and other forms of signal distortion. And it will double as a scope for any analog circuits you attach to the PICs.

You want digital, because the storage capability allows the scope to "freeze" the waveform display. You want at least two channels, so that you can see relative timings between signals. Two channels are sufficient, although occassionally, it's nice to have another channel.

100 MHz bandwidth should be more than enough for PICs. How low your bandwidth can be depends on the maximum speed you will run your PICs, or any other digital projects you work on.
Posted on 2006-04-15 19:46:49 by tenkey
Tenkey,

I'm generally using a 20mhz resonator for timing with my PICs, and don't think I'll be using a scope for anything more advanced than this.
Posted on 2006-04-15 21:32:25 by The Dude of Dudes

If you can, try to obtain an oscilloscope with more than one 'trace', ie dual trace, and make sure you can set the timebase on each trace separately..

Single-trace scopes are nice, but not nice enough..
Posted on 2006-04-16 02:43:15 by Homer
Or connect your circuit to a PC ;)
Posted on 2006-04-16 08:05:59 by ti_mo_n
You don't need a digital scope but I don't now what speed scopes are running nowadays.  Digital scopes cost much more also.  For a 20Mhz pic, you definitely don't need a 200Mhz scope.  In all my years of designing circuits, I never had one higher than 100Mhz and that is what I would have bought for myself in the past.  Right now I've got an unused 20Mhz. 

A logic analyzer is nice if you had money to burn along with a lot of signals that needed timing.  They can be used with modules for tracing running programs in assembly, too.  But, again, you won't need one for a pic.
Posted on 2006-04-16 14:30:33 by drhowarddrfine
Will an analog scope accurately display a digital (square) waveform? Analog storage scopes are much more affordable than digital. If my PIC is running at 20mhz, will a 20-30mhz scope be sufficient?
Posted on 2006-04-16 21:17:33 by The Dude of Dudes
Everything is analog.  Even "digital" oscilloscopes.  A digital scope samples analog data and converts/stores it in memory just like a computer.  An analog scope has continuous sampling and display of the input signal so it will capture everything in between the digital scopes sampling times.  So you will more likely see any harmonics or ringing on the edges of the digital edges.

iirc, for a digital scope, you would need one that samples at 80Msamples/sec to achieve the same as a 20Mhz analog scope.  (The Nyquist theorem)

Using a 20Mhz scope may have the transitions close together and the edges might get rounded a little but it might be fine for your needs.  If it's rated for 20Mhz then it should display a 20Mhz signal but the quality of the scope is what matters.
Posted on 2006-04-16 21:41:27 by drhowarddrfine
You might be interested in this webcast.
Posted on 2006-04-17 12:06:28 by Dr. Manhattan
hi,
    Get a second-hand 200Mhz with 4 channel digital storage scope will cost no more than 200$,searching them from the college ,or labs,or some electrical equipments sales or your local bbs,if you don't care for lack of mannual or probe.
    RGS!
Posted on 2006-04-26 07:13:21 by Luckrock
  Hell if you can afford it, get a Techtronics
Posted on 2006-07-18 12:13:27 by mrgone