Broken quadrature encoder circuit on TI F281x DSPs?

[Dave Hansen]

On Thu, 25 Aug 2005 16:32:52 -0300, Ricardo
<spamgoeshere1978@yahoo.com> wrote:

Dave Hansen escreveu:
On Thu, 25 Aug 2005 10:17:05 -0700, Chris Carlen
crcarleRemoveThis@BOGUSsandia.gov> wrote:
snip
N-1 N 0 1 2 3 4 5 ...
______ ______ ______ ______
B: ______ ______ ______ ______
___ ______ ______ ______ ___
A: ______ ______ ______ ______
______
Z: __________________ ________________________


This looks right here.

The quote looks right here, too, though my original post had one more
space on each of the upper lines (and the numbers line). I'm not sure
where that space went. Or where it came from, assuming the OP was
correct.

Regards,

-=Dave
--
Change is inevitable, progress is not.

 

[Jerry Avins]

jmeyer@nowhere.net wrote:

...

Read over United States Patent 4300039, then we'll correspond further.

Jerry


Dear Jerry,
It is seldom necessary to quote an entire message filled with timing
diagrams and diatribes simply to add a one line reply.

Jim,

Seldom, certainly. In this case, there was a purpose. I doubted that
those diagrams represented what the OP wanted to show, so I thought it
would be well for him to see them as they appeared in my reader.

I missed the diatribe. What I saw was a rather lengthy tale of woe.

Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ

 

On Thu, 25 Aug 2005 07:51:59 -0700, Chris Carlen
<crcarleRemoveThis@BOGUSsandia.gov> wroth:

jmeyer@nowhere.net wrote:
Dear Jerry,
It is seldom necessary to quote an entire message filled with timing
diagrams and diatribes simply to add a one line reply.


Interesting combination huh, "timing diagrams and diatribes."

:-D

I only calls 'em like I sees 'em.

Jim

 

On Thu, 25 Aug 2005 10:17:05 -0700, Chris Carlen
<crcarleRemoveThis@BOGUSsandia.gov> wroth:

So things like this look right:

N-1 N 0 1 2 3 4 5 ...
______ ______ ______ ______
B: ______ ______ ______ ______
___ ______ ______ ______ ___
A: ______ ______ ______ ______
______
Z: __________________ ________________________

The edges of B and Z waveforms line up vertically, and the numbers above
are centered within 1/4 cycles of the waveform.

The only way to resolve this problem is to post screen captures of what
*we* see when we look at your message. I've started the ball rolling by posting
"Diatribe.jpg" to ABSE.

O wad some power the giftie gie us To see oursel's as ithers see us! It
wad frae monie a blunder free us. And foolish notion; What airs in dress and
gait wad lea'e us, And ev'n devotion! (R. Burns)

Jim

 

On Thu, 25 Aug 2005 18:28:31 GMT, "Jona Vark" <noemail@all.com> wroth:

How petty.. it si a QUADRATURE encoder. The waveforms are all the same.. If
you've seen one.

It si?

Jim

 

[Jerry Avins]

Chris Carlen wrote:

Jerry Avins wrote:

Read over United States Patent 4300039, then we'll correspond further.

Jerry



Thanks for the input Jerry.

I am aware of such methods. I wish to avoid building my own quadrature
decode hardware. I could do it if I want, and would probably do it with
a state machine in a FPGA that I plan to have nearby the DSP for misc.
logic tasks.

Instead of a state machine, you can use a flip-flop and 2 XORs. If the
tracks can interrupt when going positive and negative, that can all be
software, with the "flip-flop" being the LSB of the counter.

But the reason I want to rely on the F281x QEP circuitry is that I will
be using the compare match function as well. Also period interrupts. Of
course, all this can be done as well with the PLD, but if I can make the
DSP's circuitry work, then that's the most straightforward path.

I don't know the QEP effects.

It turns out that while I think they did blow it in terms of the most
sensible implementation, I can get working results with just a minor
external hardware trick.

Have you considered what happens when vibration moves the counting track
back and forth across a transition without actually causing any net
rotation?

If I simply can guarantee that the Z rising edge occurs after the
condition A=B=1 is satisfied, as well as setting the counter period to
the encoder's max count, then actually I can't ever get an extra count.
The only deficiency is that it can only sync to absolute position in
one direction. But that is fortunately not a bog problem in this
application.

I think you can resolve the ambiguity by looking at transitions of all
tracks at both ends if the Z pulse.

Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ

 

[Jerry Avins]

Jim Granville wrote:

...

Not sure I'd call Nov 10 1981 'new' ?
XOR based quad solutions have been around a very long time :
You need either a pulse generator ( hard in an ASIC, or FPGA)
or some FF's, and a faster clock, to do effectively the same thing.
In today's digital fabric, the FF's are cheaper, and simulate
correctly, and avoid issues with clock domain crossing...
to .

The only pulses are generated by the encoder. I don't know what you mean.

Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ

 

[Jerry Avins]

John Woodgate wrote:

...

The diagram seemed to make sense to me when displayed in Courier New. So
I have no reason to assume that the OP used a proportional font. YMMV, I
suppose.

It could have been worse. A dash is a dash, so there was only a little
displacement between successive lines. But consider his labeling:

N-1 N 0 1 2 3 4 5 ...
______ ______ ______ ______
B: ______ ______ ______ ______

I suppose he meant something like

N-1 N 0 1 2 3 4 5 ...
______ ______ ______ ______
B: ______ ______ ______ ______


Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ

 

[Tony Williams]

In article <dekueh01n4s@news2.newsguy.com>,
Chris Carlen <crcarleRemoveThis@BOGUSsandia.gov> wrote:

So things like this look right:

N-1 N 0 1 2 3 4 5 ...
______ ______ ______ ______
B: ______ ______ ______ ______
___ ______ ______ ______ ___
A: ______ ______ ______ ______
______
Z: __________________ ________________________

The edges of B and Z waveforms line up vertically, and the
numbers above are centered within 1/4 cycles of the waveform.

Below is the diagram from your original post. I put it into
a hex editor. All "s" chars below are where there was a 20H
(space char) and the 0A char is your newline. I've also
added a blank line between waveform pairs of lines.

ssssssssss______ssssss______ssssss______ssssss______0A
B:s______ssssss______ssssss______ssssss______0A

ssss___ssssss______ssssss______ssssss______ssssss___0A
A:ssss______ssssss______ssssss______ssssss______0A

ssssssssssssssssssssss______0A
Z:s__________________ssssss________________________0A

You will see that on all lines where the first character
is a space, then an extra space has been added. I think
this was done by your newsreader when you generated the
post. AFAIK this is a characteristic of some newsreaders.

Conversely when reading your post, some newsreaders will
drop the extra space (when it is the first char on a line),
whereas others will not.

For example, in Turnpike (same newsreader as JW) your post
lined up perfectly, whereas in this newsreader (Pluto) the
one-space-offset is kept and displayed.

I suspect this is why Fred Bloggs and Win Hill post ascii
diagrams with dummy chars as the leading chars on each line.

As a matter of interest, all my typed text here has a leading
space on each line. Do you see that space or not?

--
Tony Williams.

 

[Chris Carlen]

Tony Williams wrote:

Below is the diagram from your original post. I put it into
a hex editor. All "s" chars below are where there was a 20H
(space char) and the 0A char is your newline. I've also
added a blank line between waveform pairs of lines.

ssssssssss______ssssss______ssssss______ssssss______0A
B:s______ssssss______ssssss______ssssss______0A

ssss___ssssss______ssssss______ssssss______ssssss___0A
A:ssss______ssssss______ssssss______ssssss______0A

ssssssssssssssssssssss______0A
Z:s__________________ssssss________________________0A

You will see that on all lines where the first character
is a space, then an extra space has been added. I think
this was done by your newsreader when you generated the
post. AFAIK this is a characteristic of some newsreaders.

Conversely when reading your post, some newsreaders will
drop the extra space (when it is the first char on a line),
whereas others will not.

For example, in Turnpike (same newsreader as JW) your post
lined up perfectly, whereas in this newsreader (Pluto) the
one-space-offset is kept and displayed.

I suspect this is why Fred Bloggs and Win Hill post ascii
diagrams with dummy chars as the leading chars on each line.

As a matter of interest, all my typed text here has a leading
space on each line. Do you see that space or not?

Yes, I see leading spaces on your text, not on your timing diagrams with
spaces mapped to "s".

I also see that the waveforms are not appearing to you as I see them.
Interesting. It seems that spaces are not a reliable means of spacing
ASCII diagrams in news posts.

Unless as you mention about Win's posts, one puts a leading non-space
char on each line?

Thanks for the input. I was begining to think folks were going
overboard in hashing the issue. But now I have learned something.

Good day!




--
_______________________________________________________________________
Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA
crcarleRemoveThis@BOGUSsandia.gov
NOTE, delete texts: "RemoveThis" and "BOGUS" from email address to reply.

 

[glen herrmannsfeldt]

Tony Williams wrote:

(snip)

Below is the diagram from your original post. I put it into
a hex editor. All "s" chars below are where there was a 20H
(space char) and the 0A char is your newline. I've also
added a blank line between waveform pairs of lines.

ssssssssss______ssssss______ssssss______ssssss______0A
B:s______ssssss______ssssss______ssssss______0A

ssss___ssssss______ssssss______ssssss______ssssss___0A
A:ssss______ssssss______ssssss______ssssss______0A

ssssssssssssssssssssss______0A
Z:s__________________ssssss________________________0A

You will see that on all lines where the first character
is a space, then an extra space has been added. I think
this was done by your newsreader when you generated the
post. AFAIK this is a characteristic of some newsreaders.

Conversely when reading your post, some newsreaders will
drop the extra space (when it is the first char on a line),
whereas others will not.

It came out fine on Netscape 7.1.

-- glen

 

[Rich Grise, but drunk]

On Thu, 25 Aug 2005 19:29:11 +0000, Jonathan Kirwan wrote:

On Thu, 25 Aug 2005 17:52:23 GMT, iddw@hotmail.com (Dave Hansen)
wrote:

On Thu, 25 Aug 2005 10:17:05 -0700, Chris Carlen
crcarleRemoveThis@BOGUSsandia.gov> wrote:

[...]
So things like this look right:

N-1 N 0 1 2 3 4 5 ...
______ ______ ______ ______
B: ______ ______ ______ ______
___ ______ ______ ______ ___
A: ______ ______ ______ ______
______
Z: __________________ ________________________

Almost, but not quite lined up when it got here. It looks like either
the upper lines gained a space, or the lower ones lost one. If I make
a minor correction, I get:

N-1 N 0 1 2 3 4 5 ...
______ ______ ______ ______
B: ______ ______ ______ ______
___ ______ ______ ______ ___
A: ______ ______ ______ ______
______
Z: __________________ ________________________

Exactly correct. Now it looks right. You've identified the issue, I
think.

Which at least appears correct on my system. FWIW, if I were drawing
it, I'd put in the vertical markers, and try to line the numbers up on
them, e.g.

N-1 N 0 1 2 3 4 5 ...
_____ _____ _____ ______
B: _____| |_____| |_____| |_____|
__ _____ _____ _____ ___
A: |_____| |_____| |_____| |_____|
_____
Z: _________________| |________________________


This would have made it easier for me to follow, anyway...

Neat. I like it much better, too.

Jon

<AOL>
Me, Too!
</AOL>

%-}
Rich