LPC11U24/LPC1347 JTAG/SWD debugging with LPC-Link

23. September 2013 21:41 by Jens Willy Johannsen
Categories: ARM

I had some problems getting my ROV on-board controller (which uses a LPC1347) programmed from LPCXpresso.

After doing the research I should have done before I had the PCBs made (doh), I found out I had messed up the SWD programming/debugging connections.

And so, in order to spare anyone else the same trouble, here is a small recap of which wires to connect to what.

Connections from LPC11U24/LPC1347

These are the minimal connections from the MCU to the LPC-Link:

Pin name LQFP48 pin no. Connect to
#RESET/PIO0_0 3 SWD pin 10 (#RST)
SWDIO/PIO0_15/AD4/ 25 CT32B1_MAT2 39 SWD pin 2
SWCLK/PIO0_10/SCK0/CT16B0_MAT2 29 SWD pin 4

Note: It is not necessary to have pull-up resistor on #RESET (or any other pin) unless other parts of the circuit might affect the levels since it is internally pulled up to VDD.

Connections from JTAG/SWD

These are the minimal connections from the LPC-Link to the MCU board.

Pin number Connect to LQFP48 pin no. Comment
1 3.3V on MCU 8, 44
2 SWDIO 39
3 n/c Optional GND (see note 1)
4 SWCLK 29
5 n/c Optional GND (see note 1)
6 n/c Optional SWO (see note 2)
7 n/c
8 n/c
9 GND 5, 41
10 #RESET 3

Note 1: It is sufficient to connect one of the GND pins (e.g. SWD pin 9) as pins 3, 5 and 9 are all connected on the LPC-Link.

Note 2: SWD pin 6 can be connected to PIO0_9/MOSI0/CT16B0_MAT1/SWO (LQFP pin 28) but this is not required.

Pin numbering

This image shows the pin numbering on the LPC-Link. Pin 1 has been marked in red.

Do yourself a favor and perform a continuity check from the LPC-Link side to your MCU board to make sure which pins go where.

LPC-Link pinout

LPC-Link pinout

(Image composited from images from and

Be aware that the 0.1" pins on the right edge of the board do not follow the JTAG pin numbering but have these connections:

  1. VCC
  2. SWDIO
  3. SWCLK
  4. SWO
  5. TDI
  6. #RESET
  7. EXT. PWR
  8. GND

The required pins are 1, 2, 3, 6 and 8.

Connection procedure

Sometimes LPCXpresso can't initialize the LPC-Link even though it is connected. I have found that following the following procedure works every time:

  1. Launch LPCXpresso IDE
  2. Power up device
  3. Attach to LPC-Link
  4. Connect LPC-Link to computer by USB
  5. Debug firmware from LPCXpresso
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