10 pin ARM Cortex JTAG

Development Boards MicroMod
1

Anyone know what to do with the KEY signal on a 10 pin connector? I’ve seen suggestions it can just be grounded, but I’m concerned this might short out a programmer. (I use a Flyswatter 2 with OpenOCD)

In the past I’ve used 20 and 14 pin JTAG but would like to reduce it to 10 to save board space (without going Tag-Connect) and fall in line with current recommendations.

This is for an LPC4078. Three options I can think of:

  • Leave it floating

  • Ground it

  • Connect it to P2.10, the ISP enable pin (which currently has a weak 100k pullup on my board since I don’t ever use the boot ROM).

I have a vague suspicion it’s really intended for the third option… but if NOT and I connect it there it could make the board get stuck in the ISP on boot.

I can’t seem to find ANY documentation discussing this…

Anyone know?

Will OpenOCD ever use it?

Is it electrically connected when adapted to a 20 pin programmer like the Flyswatter 2?

2

Also, I’m concerned if it’s an ISP enable it would be held high unless trying to enter ISP. If I ground it this would not be so great and might cause the programmer to shutdown on overload if it shorts (FT2232R I believe is what the FS2 uses, not sure if it’s buffered).

3

Looking at the schematic for the Olimex 20-to-10 adapter, they run this through an unpopulated resistor, so I guess I can just ground it. (That’s the adapter I use.)

What about GNDDetect? Another pin to just ground?