AVR Dragon question

Dave · Joined: 05 Feb 2005 Posts: 314 Location: OR

Hello

I'm trying to get started with XMega chips and it's not going well. I'm using a new AVR Dragon programmer and a ATXMEGA256A3U with the PDI connections. The programmer will not recognize the micro until I connected my scope probe to the CLK line, then read/writes are possible. All power pins are bypassed with 0.1uF caps. I've tried pullups/pull downs on the clk, data lines, still does not work unless the scope probe is connected.

I think the problem is with the Dragon, so my question is: Has anyone had a success or problems using the Dragon with Xmega parts?

Dave

Paulvk · Joined: 28 Jul 2006 Posts: 1257 Location: SYDNEY

I would try a 1K resistor to ground as I think the probe is putting a load accross the line.

Regards Paul

Dave · Joined: 05 Feb 2005 Posts: 314 Location: OR

Paul,
Thanks for the input. I did try both pull up and pull down resistors (15K). The scope probe has 10M impedance so 1K seems a bit low to me.

I found this known issue for the JTAGICE3.

hgrueneis · Joined: 04 Apr 2009 Posts: 902 Location: A-4786 Brunnenthal

Dave,
how much is the undershoot?
If it is more than 0.2 Volt, then a Germanium diode to ground might help to limit the negative going voltage.
The problem with the capacitor is, that it also deforms the rest of the signal.
The diode will just add a few pF.
Hubert

Paulvk · Joined: 28 Jul 2006 Posts: 1257 Location: SYDNEY

If its undershoot try a 180 ohm resistor in series with the line, this problem I came accross with the ENC28J60 and series resistors were the recomendation in the spec.

Regards Paul

hgrueneis · Joined: 04 Apr 2009 Posts: 902 Location: A-4786 Brunnenthal

One more thing I just thought of.
The scope pobe cable probably has a capacitance of 100 to 300 pF per meter depending on the type of coax cable.
Hubert

edit:
If you need to measure timing on a high frequency low impeadance signal, just twist a few turns of wire around the signal wire and scope that.

Dave · Joined: 05 Feb 2005 Posts: 314 Location: OR

Here is a pic of the clk and data lines. I suspect that there is a conflict in the data line during a change of input/output direction.

It is working now but that clk signal does not look good to me. I've ordered a programmer off ebay that is made here in Oregon so I should get it very soon. I'll let you know how that works out.

Dave

Dave · Joined: 05 Feb 2005 Posts: 314 Location: OR

This is from the AVR Dragon user guide.

Dave · Joined: 05 Feb 2005 Posts: 314 Location: OR

Paul, Hubert

I added a 120 ohm resister in series with the clk and it reduced the undershot by about 50%. It still needed the 100pF cap to gnd. but if my new programmer doesn't fix the problem I will continue to use a series resistor and add a germanium diode.

Thanks for your suggestions it is very appreciated.
Dave

Paulvk · Joined: 28 Jul 2006 Posts: 1257 Location: SYDNEY

Great dave so microchip do know what they are talking about, try a 1K resistor and see what happens its not the resistance I am thinking about its the added inductance due to the spiral cut on the resistor being longer also a ferrite bead over one end of the resistor could also be tried.

Regards Paul

Dave · Joined: 05 Feb 2005 Posts: 314 Location: OR

Here are the results of tests using my new AVRISP MKII compatible programer.
1. The new programer also requires a cap to ground on the clk line. Without any cap it fails. (100pF).
2. The clk frequency is half that of the AVR Dragon but the clk wave form is much better on the new programer.
3. The new programer seems to read/write faster then the dragon. I didn't measure the actual time this is just my perception.
4. The new programer reads the rev no. of the Xmega a "G". Which matches the rev no on the back of the part. The dragon read this as A.

So for now I'll continue to use the new AVRISP MKII compatible.

I would still like to know what programers others are using for xmega parts. I guess I need to start a new thread to get that question answered.

Dave

nil_orally · Joined: 07 Jun 2010 Posts: 18

Hi Dave,

I have 4 different boards with that we use about 30 a month of (it varies) with ATXMEGA32A4 on. We just use a AVRISP mkII. The boards do not need any components to allow programming.

PeterM · Joined: 09 Jun 2008 Posts: 118

If you want a to use an AVRISP MKII you can't beat the original Atmel version, they are cheap (less that $50)
not worth the hassle of using a Chinese clone.

I also had issues using an AVR Dragon, at the end it failed so I sent it back for a refund and bought an AVRISP MKII.

Dave · Joined: 05 Feb 2005 Posts: 314 Location: OR

I should have done more research before buying the Dragon and bought a AVRISP MKII in the first place.

Oh well, live and learn.

Thanks guys,
Dave