Can anyone tell me what these ports are for, or what they do?

  • 6
    \$\begingroup\$ Those are pads for a header connector, which is not stuffed. Probably some sort of debug or test interface. \$\endgroup\$ – John D Apr 10 '15 at 18:54
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    \$\begingroup\$ "Can anyone tell [...]?" I doubt anyone could tell. No schematic, no idea how this this connector is wired, no knowledge of where this board came from. One can only wildly guess. The question is unclear. \$\endgroup\$ – Nick Alexeev Apr 10 '15 at 19:14

There is no way that anyone can tell you what that is, other than "an unpopulated 2x5 header footprint". Chances are it has to do with debugging or programming the main chip. It may be (but not limited to):

  • JTAG interface
  • Custom ICSP interface
  • Serial (UART) interface for console

It's unlikely to be JTAG since the pinout doesn't look quite right to me.

  • Pin 9 is GND, on JTAG it's usually pin 10.
  • Pin 10 looks like it may be VCC by the thickness of the trace. On JTAG that's usually pin 4.
  • Pins 3 and 5 look like data pins with pull-up resistors. JTAG has 4 pins you might want to do that to, not just 2.

So my money is on either the custom ICSP or the UART interface - most likely the UART interface (pins 3 and 5 would be TX and RX, or the other way around).

I'm guessing that's a Ralink chip, probably in a router? My second guess is that you're probably looking for the console connection to allow you to install OpenWRT on it. Am I close?

  • \$\begingroup\$ How do you recognize where is pin 1? Does the square pad always represent GND ? \$\endgroup\$ – Al Bundy Apr 10 '15 at 20:14
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    \$\begingroup\$ Pin 1 is identified 4 ways there. 1: It's the square pin. 2: It's the one by the big dot. 3: It has a triangle pointing at it. 4: It's the one by the chamfered corner of the ident outline. \$\endgroup\$ – Majenko Apr 10 '15 at 20:15
  • \$\begingroup\$ So I was wrong and there is no standard for square pad to be used to identify GND ? \$\endgroup\$ – Al Bundy Apr 10 '15 at 20:19
  • \$\begingroup\$ None whatsoever. The main identifying factor for ground is the pad that's connected to what I assume to be a ground plane by thermal relief (pin 9 - the bottom-right pin) which looks a bit like a flower. \$\endgroup\$ – Majenko Apr 10 '15 at 20:21
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    \$\begingroup\$ @AlBundy To be clear, there is a strong convention that the square pin is always "Pin 1". \$\endgroup\$ – bitsmack Apr 10 '15 at 20:54

Since it's in the shape of 2x5 IDC connector, it's probably a JTAG programming header.


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