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PICList Thread
'recording of digital signals'
2009\04\21@084553 by olin piclist

face picon face
Peter Feucht wrote:
> I'm in desperate need of a small tester to check digital (5V level)
> signals with a resolution of 1µs.

So this is a one-off?  If so, it sounds like a PIC managing a shift register
and some static RAM will do the trick.  Once the data has been captured, you
send it to the host via USB.

I had to do something similar once and used the MSSP in synchronous mode to
receive the serial data.  The PWM module produced the sample clock, which
was looped back to the MSSP clock input.  The processor only had to deal
with whole 8 bit bytes.  Back then the top of the line PIC was the 16F877,
and every instruction mattered.  Today you can use a 18F2550 at 12MHz
instruction rate, which gives you 144 instruction cycles per 8 bit data
byte.  That's plenty to grab it from the MSSP and write it to a external
RAM.  After the capture is over, the 18F2550 can then switch modes and dump
the RAM contents to the host via the USB.

If you're the only device on the USB, then maybe you can dispense with the
RAM and dump straight to the USB.  Use the CCP and MSSP modules to capture
the data stream 8 bits at a time as above, then use the MSSP interrupt to
write data bytes to a FIFO.  The foreground code meanwhile sits in a loop
reading from the FIFO and writing to the USB.  Your data rate is only
125Kbytes/sec, so the system really should be able to handle this.

If this is a one-off, my ReadyBoard-02 might be handy
(http://www.embedinc.com/products/ready02).  It comes with the 18F2550 and
all the stuff around it to power it and make it run.  It also somes with
generic USB firmware and host software that sets up pipe 1 as a
bi-directional stream of bytes.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2009\04\21@091802 by Tamas Rudnai

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On Tue, Apr 21, 2009 at 2:10 PM, Peter Feucht <
spam_OUTp.feuchtTakeThisOuTspampalmed-medizintechnik.de> wrote:

> One more question: How is a device called which does stuff like I have to
> have? I cannot believe that I'm the only one who needs to analyze digital
> signals....
>

Hi Peter,

I am not quite sure your specs, however, you might want to look for "data
acquisition" or "logic analyser".

Tamas
--
http://www.mcuhobby.com

2009\04\21@095838 by Alan B. Pearce

face picon face
>I am not quite sure your specs, however, you might want
>to look for "data acquisition" or "logic analyser".

Or 'data logger' or maybe even 'digital data logger'.

So many names for one lot of functionality ... ;)))

2009\04\21@134003 by Jon Chandler

picon face
Alan B. Pearce wrote:
>> I am not quite sure your specs, however, you might want
>> to look for "data acquisition" or "logic analyser".
>>    
>
> Or 'data logger' or maybe even 'digital data logger'.
>
> So many names for one lot of functionality ... ;)))
>  
Would the logic analyzer function of the PICKIT II work here?  Three
channels, reasonable on-screen display and only $39.


Jon


2009\04\21@142311 by Peter Feucht

flavicon
face
Jon,
thanks for your proposal, but this will not work for I have to store 12
seconds of data. Do you know of any possibility to expand the pickit's
storage width?

Peter





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