Connecting Red Probe+ to the MCU of an LPCXpresso board

The LPCXpresso board was not designed with connecting an external probe, such as Red Probe+, in mind. However it is relatively straight forward to do so.

Note in particular that you cannot just connect a Red Probe+ to the debug connector (J5) on the LPCXpresso board. The J5 debug connector is output only - it is designed to allow the LPC-Link of the LPCXpresso board to debug an external board.

Splitting the LPCXpresso board

Before you can connect your Red Probe+, you will need to split the MCU portion of your LPCXpresso board from the LPC-Link portion. Details of how to go about doing this can be found in the FAQ Debugging another board using an LPCXpresso board's LPC-Link.


Before making modifications to your LPCXpresso board and connecting your Red Probe+, you may wish to check the schematics for the actual LPCXpresso board variant that you are using. NXP currently have schematics available from:

Debug connection

Having split your LPCXpresso board, you will then need to connect the Red Probe+ to the MCU portion of the LPCXpresso board as follows:

LPCXpresso board

20 pin Red Probe+ connector



JTAG_TMS   - J4-4

 P7 - TMS


 P9 - TCLK

JTAG_TDO   - J4-8

P13 - TDO

JTAG_TDI   - J4-10

 P5 - TDI

GND        - J4-16

P20 - GND

Note that details of the Red Probe+ debug connector can be found in the FAQ SWD/JTAG connectors and pinout.

Typically, pin 1 of the 20-way Red Probe+ cable is indicated by the "red stripe".


The MCU portion of the LPCXpresso board is usally powered from the LPC-LINK end of the board. When the connections across J4 are cut, you need to have another power source for the target. 3v3 can be supplied to J6-28 and GND to J6-1.

ExtProbe2LPCXpresso (last edited 2013-03-18 17:37:58 by CrSupportAb)