Jtag - dual use

[lpcware]

Content originally posted in LPCWare by brownm on Wed May 22 03:47:05 MST 2013

Hi there

We are designing a product and are one pin short on the LPC812, normally we keep the defined JTAG pins free so that we are able to access the device via jtag at any time via the dedicated (default Pin 0_2 & 0_3) pins. Howver in this case we would like to use one of the Jtag pins (SWCLK) for a blinky LED, nothing too important while we are actually doing the debug, but if we change the function of this pin will we be able to get access to the device via the JTAG after programming it the first time?

Thanks and Regards

Marshall Brown

[lpcware]

Content originally posted in LPCWare by brownm on Wed May 22 12:27:06 MST 2013

That's great - thanks for the clear consice response.

Regards

Marshall

[lpcware]

Content originally posted in LPCWare by TheShed on Wed May 22 06:42:01 MST 2013

The short answer is - No.

Once you have switched the P0.3 from SWCLK to GPIO (PINENABLE0 register) it is no longer available for SWD debug. You will need to load a different code image that leaves P0.3 in the default  state to be able to use the SWD port.

Just make sure you have access to the ISP pins to re-program the flash - and be careful about what you attach to P0.1. ;-)

EDIT: Leon is correct in that the hardware itself should not be a problem,..

--

mike

[lpcware]

Content originally posted in LPCWare by leon_heller on Wed May 22 04:08:44 MST 2013

You should be OK. Most JTAG adapters should be able to drive the pin as well as an LED.