dragon buffer

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Hello,

i recently bought a dragon for debugging, including externally powered usb hub, a few cables and now i want to make a buffer with 74hc08 from Plons site
http://www.aplomb.nl/TechStuff/Dragon/Dragon.html.
What i don't get is the point of wiring target jtag, spi and debugWire pins together, i mean, what is the purpose of dragon spi pins then, if it can stay unconnected and we can drive target spi with dragon jtag?
I found some more information, including this
http://www.atmel.com/Images/doc2562.pdf
, but it didn't get clearer.
And also it seems that info about dragon is pretty scarse.

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Take an Ohm-meter and measure between JTAG connector SCK and ISP connector SCK on the DRAGON. You'll find 0 Ohm: it's the same signal !

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Plons wrote:
Take an Ohm-meter and measure between JTAG connector SCK and ISP connector SCK on the DRAGON. You'll find 0 Ohm: it's the same signal !

i am really lost now :) How can jtag and isp sck be the same if jtag is using dragon clock and isp uses avr internal or external oscillator?

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The AVR is using the internal clock yes, but the programming interface uses it's own clock to shift in the programming data. ISP does not use the AVR clock, but it does have to be no greater than 1/4 the AVR's clock.

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Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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Hi man. So is it somehow an exeption or a special case?
From datasheets

Quote:
When using the SPI algorithm, the clock used during programming is supplied from either the
AVR Internal RC Oscillator or from an external crystal / resonator. The programming SPI
speed is completely dependent on the speed of this oscillator.

I just want to know most of things before touching my humble and sensitive dragon :)

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Then Don' touch it. I have one of the originals Digikey sold and knock on wood I have never had an issue with it.

If you are so worried about it make a little PCB with 220 ohm resistors in series with all the lines except GND, VTG, and RESET. Thats what I did and it provides all I need for protection from accidentally connecting the lines directly to VCC or GND.

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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I'll do that, thanks.