(atmel) ISP pinout / ribbon plug notch confusion

[Red Squirrel]

Looking at the pin out online, like here for example:

http://www.equinox-tech.com/products/details.asp?ID=362

The SCK pin is where the notch is in the actual plug on the ISP or device I would create.  However, on the actual ribbon cable, the other end of the cable the notch is actually on the Mosi side.  Does this make sense? I'm designing a basic circuit with an Atmega and want to include a programming header for in system programming and mark where the notch would go so I can know how to plug it in, but it seems the top and bottom pins are swapped at the other end of my ISP cable.  Does this make sense?  I tested continuity to see how the pins correspond on the ribbon cable.  In the picture where you see I plugged a 3 pin header, the pins correspond on both sides of the cable, ex: from top to bottom.



Maybe I'm just getting a brain fart here, but this seems confusing that they end up being swapped.

[sleemanj]

6 pin, notch is SCK on the target.

At the programmer end, well that's up to your programmer and it's cable, as long as it makes SCK come out at the notch at the target end that's all you care about (well, that and making sure you haven't inverted the board side so VCC and GND are reversed).

[sleemanj]

This will help you get it straight (it's what I always double check against myself), a 6 Pin ISP plug (on the end of a 10-6 converter) with named pins.

[igendel]

Here it is from another angle - this is actually the pinout for PDI programmer-side connector, but the GND and VCC are at the same place for ISP.

Full post where the image came from: http://www.idogendel.com/en/archives/468

[dannyf]

on the actual ribbon cable

Your picture is quite fuzzy and difficult to tell. But it is much better to go by the pin numbers and see if they match. Sounds like in your case, the cable is not properly designed.

[mathsquid]

I used to have the same issue, so I finally made this drawing that I refer to when I need it.

[klunkerbus]

From what I can tell, you'd never be able to use that programmer and that cable to program a board designed with the standard ISP pinout.

Playing with brightness and contrast on the image to verify, it doesn't appear there's a notch on the MOSI side shown on the programmer connector, so it has to be on the SCK side where it normally would be.  The cable will swap the pin alignment so that pin 1 ends up where pin 6 should be, etc.  Whoever built that cable likely didn't realize it makes a difference which way the connectors go on. 

For the unaware, these connectors almost always mark pin 1 with a small triangle on the tab side of the connector body where the ribbon cable sits.  Once you realize that, it makes it pretty easy to see if pin 1 on both connectors go to the same side of the ribbon cable.  You do need to be careful though - not all board designers realize there really is a standard pin numbering scheme to these things, and they make up their own pin numbering scheme.  There's a popular LCD board for reprap 3D printers, for example, that was designed with the odd and even rows swapped, so that pin 1 and 2 are swapped, 3 and 4 are swapped, etc. No big deal as long as the same designer laid out the boards on both ends of the cable...

[Red Squirrel]

You can zoom in as well, the picture is quite big.   The 3 pins I added, was just for testing continuity from end to end.  The notch side on one end corresponds to the non notch side on the other end.  That's what is confusing me.   Is it just a badly made cable?  I can always grind off the notch on one side and add a marker or something on the other.   

[ajb]

Fun fact: the official Atmel tools (at least the JTAG-ICE3 and the ATMEL-ICE) have their target connectors reversed.  The cables they're shipped with have the connector inverted on one end so that the by the time you plug into the target it's the correct pinout.  These are of course the 50mil 10-pin ribbon cables, so it makes it extra hard to find replacements that aren't the stupid $15 combo cables from Atmel.

[Red Squirrel]

So in my case is it the cable that's faulty then?  It's kinda weird really because I would expect the pin out/notch to be on the same on both ends but it's not. 

[Red Squirrel]

I forgot about this topic and thought I would update it.

I was looking closely at the cable and did not realize these come apart, so I ended up just flipping the connector and then ensuring that the pin out is the same at both ends.  This removed the confusion when it comes to putting a header on a project as I can just go by the normal pin out.