Best 3 pin order for custom UPDI connector...

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For many years I've used what I call "inline ISP" which is basically just the 2x3 ISP connector put into a 1x6, still 100 mil.  It allows programming from either side of the board and also you can just put pin header through holes at and angle to program and avoid putting any sort of connector on the pcb.  This has worked quite well, but if I start messing with UPDI AVR"s I am thinking why waste the unused pins, so only 3 are needed.  I could retain the order and do something like 1-updi, 2-vcc, 3-gnd, but I wonder if that is the safest choice in case the connector is used in reverse polarity.  Is there a better choice?  Should the gnd be in the center?

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Seems like gnd in the center would be a good way to go...there are now some clip-ons that will touch small smd pads on the board...sorta like a finger based bed of nails to temporarily hook up the programming pins.

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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You could also go with 4 pins, with 1 of the inside pins missing (and no pcb hole) to get a 'keyed' connection. Then you don't have to deal with the 3 attempts to get it right- if it fits it must be correct. If using a 4pin female header then I guess a plug is required on the missing pin location to maintain the keyed feature.

 

oo_o

 

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Or stay with 6-pin and mirror each pin:

  1. UPDI
  2. VCC
  3. GND
  4. GND
  5. VCC
  6. UPDI

 

Really, only 5 are needed for that:

 

  1. UPDI
  2. VCC
  3. GND
  4. VCC
  5. UPDI

 

That way there's no possibility of getting it wrong.

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

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"Fast.  Cheap.  Good.  Pick two."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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With gnd in the centre you could also mount angled pins onto any Curiosity Nano board, cut off the target section and use the rest as your programmer/debugger...

 

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That would give you a pretty cheap full-blown AVR UPDI programmer/debugger (minus high-voltage support), but it wouldn't solve the polarity issue. At least you won't be able to accidentally swap GND and VCC by putting GND in the middle. Swapping UPDI and VCC shouldn't do any harm, it just won't work.

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There is a sort of standard you know...

 

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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je_ruud wrote:
Swapping UPDI and VCC shouldn't do any harm, it just won't work.

 

That is what I am looking for, I guess I'll use (1) UPDI (2) GND (3) VCC.

 

Brian Fairchild wrote:
There is a sort of standard you know...

 

I know, but half of its pins are NC...

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alank2 wrote:

Brian Fairchild wrote:
There is a sort of standard you know...

 

I know, but half of its pins are NC...

Well, if you take Brian's table, remove all NC pins and shift the numbering one to the right you end up with (1) VTG (2) GND (3) UPDI. Then you would at least not have the opposite numbering order as the "standard". ;-)

 

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What is Brian's table a standard for?

 

Isn't the Microchip/Atmel standard (1) UPDI (2) VCC (3) NC (4) NC (5) NC (6) GND ?

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alank2 wrote:

What is Brian's table a standard for?

 

It's the PICKit4 1x8 connector description. It basically describes how you connect PICKit4 to the different interfaces.

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Maybe I should go do my homework first...

I'm not familiar with the UPDI hardware interface.

Is the line impedance critical?

 

If not, perhaps you could put a 300 ohm resistor in series with the UPDI pin, (it would take minimal PCB space).

Then if you did connect it backwards, and connected Vcc to the UPDI pin, you would at least not fry the UPDI pin if it was attempting to drive low.

With short programming cables, and relatively low speed signals, the extra Resistance, (and line Capacitance), would hopefully be minimal enough not to significantly distort the programming signal.

 

JC

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DocJC wrote:
Is the line impedance critical?
Less so for UPDI than PDI (900KHz max versus 30MHz max) (one-wire UART versus USART)

Some of the very inexpensive UPDI programmers have significant impedance.

 

"Dare to be naïve." - Buckminster Fuller

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"Dare to be naïve." - Buckminster Fuller