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From: Nial Stewart on 17 May 2010 04:49
> - the target should have the female connector,
> less likely to be damaged. OTOH, the probe has the
> male pins and they can be easily damaged so I plan
> interchangeable/disposable headers. It's better
> to spend a fraction of dollar on a new probe header
> than to fix an existing board :-/

It's probably also the case that it's the female side of the
pair that fails first, a male probe header will last longer
than a female.

On the other hand putting females on the board is probably more
expensive. Having said that if cost is that sensitive you'll
probably be using test probes as below...

> - spring-loaded test probes are also great :
> they're 10 or 100x more expensive per pin
> but there is no part to solder on the target,
> no hole to drill or height problem.
> Well, it's extreme, right...

Is it that extreme? It isn't much hassle adding probably test
points to allow the option of no-fitting he headers and probably
wouldn't be too hard making a jig to hold the bits.

You wouldn't have to get full a bed of nails jig done.

>> Come on Altera (and the rest), give us a standard.
> don't count on them to "give" a "good" standard ;-)
> they're in for the money, they follow the money...

Aye, but it's getting to the stage where an FPGA and programming
memory footprint is matched by the programming header!

It could start to affect device selection.


Nial.



From: Ed McGettigan on 17 May 2010 15:17
On May 17, 1:49 am, "Nial Stewart"
<nial*REMOVE_TH...(a)nialstewartdevelopments.co.uk> wrote:
> >> Come on Altera (and the rest), give us a standard.
> > don't count on them to "give" a "good" standard ;-)
> > they're in for the money, they follow the money...
>
> Aye, but it's getting to the stage where an FPGA and programming
> memory footprint is matched by the programming header!
>
> It could start to affect device selection.

Are you serious?

I don't think that Xilinx, Altera or ARM really care what header is
used on the target board. Each of use picked something that we think
makes sense and provided a ribbon cable that mates the JTAG cable to
the target board.

Nothing prevents you from using an alternative connector on the target
board and creating an adapter that connects to the JTAG cable.

Ed McGettigan
--
Xilinx Inc.

From: Nial Stewart on 17 May 2010 15:58
> > It could start to affect device selection.

> Are you serious?

Well, probably not.

> I don't think that Xilinx, Altera or ARM really care what header is
> used on the target board. Each of use picked something that we think
> makes sense and provided a ribbon cable that mates the JTAG cable to
> the target board.

It did make sense 15 years ago, but it's a bit ridiculous if you're using
0201/0402 components to have to use the behemoth 2x5 0.1" pin header.

:-)

> Nothing prevents you from using an alternative connector on the target
> board and creating an adapter that connects to the JTAG cable.

Adaptors lead to un-reliability, wires getting crossed or shorted etc.
It would be nice to have a more compact 'standard'.

The EEBlaster that Thomas linked to earlier in the thread...

http://www.entner-electronics.com/tl/index.php/eeblaster.html

....has two 'programming heads' which seems a good solution.


Nial.



From: Ed McGettigan on 17 May 2010 20:16
On May 17, 12:58 pm, "Nial Stewart"
<nial*REMOVE_TH...(a)nialstewartdevelopments.co.uk> wrote:
> > > It could start to affect device selection.
> > Are you serious?
>
> Well, probably not.
>
> > I don't think that Xilinx, Altera or ARM really care what header is
> > used on the target board.  Each of use picked something that we think
> > makes sense and provided a ribbon cable that mates the JTAG cable to
> > the target board.
>
> It did make sense 15 years ago, but it's a bit ridiculous if you're using
> 0201/0402 components to have to use the behemoth 2x5 0.1" pin header.
>
> :-)
>
> > Nothing prevents you from using an alternative connector on the target
> > board and creating an adapter that connects to the JTAG cable.
>
> Adaptors lead to un-reliability, wires getting crossed or shorted etc.
> It would be nice to have a more compact 'standard'.
>
> The EEBlaster that Thomas linked to earlier in the thread...
>
> http://www.entner-electronics.com/tl/index.php/eeblaster.html
>
> ...has two 'programming heads' which seems a good solution.
>
> Nial.

Xilinx used a 1x7 0.1" header with flying leads in the past, but now
uses a 2x7 2mm header (one side is all GND for shielding).

If the adapter is a very simple 2-layer PCB that converts the JTAG
cable connector to your favorite connector then there wouldn't be
reliability problems.

I can't tell from the EEBlaster picture if the two ribbon cables are
permanently connected to the box or not. If they are then I would be
worried about the signal integrity of the interface due to the large
stub from the unused cable. They list as one of the features "improved
signal integrity" so maybe they had some problems with this in the
past. I noticed that the PCB connector isn't keyed in any manner
which can lead to some nasty problems with inexperienced users.

There are many ways to implement this simple function and regardless
of what Xilinx, Altera or ARM does in this area someone won't be
happy. For the foreseeable future, Xilinx will be sticking with the
2x7 2mm connector. Feel free to use it if meets your needs, if it
doesn't then and adapters are simple and easy to create.

Ed McGettigan
--
Xilinx Inc.
From: whygee on 17 May 2010 20:00
Ed McGettigan wrote:
> I noticed that the PCB connector isn't keyed in any manner
> which can lead to some nasty problems with inexperienced users.
or tired, exhausted, sleep-deprived developers.
don't ask me why...

> Ed McGettigan
> --
> Xilinx Inc.
yg
--
http://ygdes.com / http://yasep.org
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