from Atmel - series resistors on programming lines

[rperkins]

Concerning the use of current limiting resistors on programming lines. Taken from AVR910, published by Atmel

To avoid driver contention, a series resistor should be placed on each of the three dedicated lines if there is a possibility that external circuitry could be driving these lines. The connection is shown in Figure 3. The value of the resistors should be chosen depending on the circuitry connected to the SPI bus.

So my thoughts are they should be there. In the case of the 9x , external circuitry is driving these lines low through a 200 ohm resistor to ground, through the .1uf cap. Taking that into consideration, the limiting resistor needs to be a low value. 100 ohms works, 220 doesnt.

Now what about no limiting resistor at all ? Yes it works . But are we risking the programmer if it is plugged into a circuit that is live and driving these pins. ?

I'm searching for the optimal value series limiting resistor in a usbasp device used to program the 9x. Also want to provide protection to the usbasp. The solution needs to work with the 9x no doubt, but I'm looking for the best all round solution for the versatile usbasp. What do you think ?

Thanks

[ShowMaster]

I haven't checked but what does the HK version use? After this Grammy weekend I'll have more home lab time to check it all out as well as try yours Randy. I'll try them on several 9Xs and my 9XR. They all have the original caps on the reset line. Never had trouble with the Turnigy or FkySky boards I've programmed the last 18 Mo so I never checked when I did the mods.
I've been busy repairing or modifying radios for locals and my projects are behind.
When paid, BTW, I work for red wine. I use it to celibate when I don't see smoke! If I do see smoke, a lot of red wine.
SM


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[jhsa]

Yeah, I've heard that fire departments from all around the world were discussing about using Red wine instead of foam and water to put fire out. They say one of the reasons that it is more effective it is because it relieves the stress of the men when fire fighting, therefore allowing them to be more efficient..

João

[ShowMaster]

After the second glass I stop using pointy tools and hot irons.
I can't leave green smiley faces with tap-a-talk, or any faces?


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[MikeB]

What you are trying to avoid is two output drivers directly connected and driving at the same time. On the 9x, the 200 ohm resistors on the switch lines avoid this, the switch does not drive the line to ground directly. With just these on the lines there is no need for any resistors on the programmer.

Mike.

[ShowMaster]

Good answer mike. I repaired a eBay programmer and it sort of worked. I replaced the 100 ohm resistor pack with jumpers as described in a post here and it works great now. I like it because it has the 3.3v option regulator the HK doesn't have. If I use it for other device programming would I want the resistors back?

I a few others so I have several of Randy's now that has the resistors. As as they all work for 9x and 9XR programming I'm good. It using them later for other non 9x projects that I'm worried about.

BTW,
Any word on what the x9d mcu is yet and if the programmer is built in and what interface we'll need?
SM


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[MikeB]

ARM/USB.

Mike.

[ShowMaster]

ARM/USB.

Mike.

Super!


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[rperkins]

What you are trying to avoid is two output drivers directly connected and driving at the same time. On the 9x, the 200 ohm resistors on the switch lines avoid this, the switch does not drive the line to ground directly. With just these on the lines there is no need for any resistors on the programmer.
Mike.

Thanks for this post. I'd spent some time thinking about it and finally wrapping my head around it. I can now see how the resistors within the 9x make current limiting resistors in the usbasp redundant. Utilizing current limiting resistors in a usbasp that is going to be used in other applications besides the 9x still has merit. Been meaning to make it back here sooner to thank you