Hi, Olin, =


thanks for your  input!

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....

Thanks and best regards

Peter


-----Urspr=FCngliche Nachricht-----
Von: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] Im Auftrag von
Olin Lathrop
Gesendet: Dienstag, 21. April 2009 14:47
An: Microcontroller discussion list - Public.
Betreff: Re: recording of digital signals

Peter Feucht wrote:
> I'm in desperate need of a small tester to check digital (5V level) =

> signals with a resolution of 1=B5s.

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.


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