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Stellaris LM4F120 LaunchPad Debug How To

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Stellaris LaunchPad Debug Options


Stellaris LM4F120 LaunchPad offers an in-circuit debug interface (ICDI). The interface was designed to help customers develop applications faster and to alleviate the need for an expensive external debug adapter.

Some customers would like to connect an existing external debug adapter to the Launchpad. We shall call this 'debug-in'.

Some customers would like to use the ICDI to program and debug their own custom boards or other evaluation kits. We shall call this debug-out.

The Stellaris LM4F120 LaunchPad's ICDI supports both of these desires. This guide will explain how.


To support either debug-out or debug-in on the LM4F120 LaunchPad you need to connect to the JTAG/SWD signals that are made accessible as test points on the LaunchPad.

Please note
The ICDI firmware only supports JTAG signaling at this time. SWD (serial wire debug) can be supported by the target as a debug-in. SWD is not supported in debug-out configuration.

A simple rugged method to make these connections is to solder a row of header pins into holes provided. The holes are spaced evenly on a 100 mil (0.1 inch) grid. Standard 0.1 inch header pins available from sources such as Digi-Key and Mouser should work well for this.

The signal meanings are listed below

JTAG test clock signal. This is also SWCLK for serial wire debug connections.
JTAG test mode select. This is also the SWDIO signal for serial wire debug connections.
JTAG test data out. This is als othe SWO signal for serial wire debug connections.
JTAG test data in.
Pull this pin low to tri-state the on board ICDI drive signals. This prevents the ICDI from interfering with an external debug-in connection.
3.3V logic level data pin. Connect to target's UART transmit signal. Optional.
3.3V logic level data pin. Connect to target's UART receive signal. Optional.
Located just above RXD. Target reset pin.
You will need to be sure that the two boards share a common ground reference. Ground connections are available on the BoosterPack expansion headers and also on the test points provided at the lower left and lower right corners of the LaunchPad.

Note: RXD and TXD are the UART connections used to interface UART0 of the LM4F120H5QR on board target through the ICDI to the virtual serial port provided on the debug USB connection. These are not standard JTAG/SWD signals. They are provided as convenience and can be used in debug-out or debug-in scenarios.


Use the following steps to use the ICDI to program and debug an off-board device.

  • Remove the power jumper located just below the green power present indicator LED. This guarantees that the on board LM4F120H5QR is not corrupted by the debug signals. It also prevents the LM4F120H5QR from interfering with the debug signals.
  • Connect the JTAG signals to your target processor.
  • Connect a common ground reference between the two systems.
  • Optionally connect the RXD and TXD pins to connect your target UART to the ICDI virtual serial port.

Your ICDI is now ready to perform JTAG operations on the off board target processor.


Use the following steps to connect an external debug adapter to the on board LM4F120H5QR.

  • Connect the JTAG signals from your debug adapter to the LaunchPad.
  • Ground the EXT-DBG pin to be sure the ICDI does not interfere with the external adapter.
  • Optionally connect RXD and TXD to connect the on board LM4F120H5QR to an off board UART.

Your external adapter is now ready to debug the on board LM4F120H5QR.

For greater details on what is required to perform DEBUG IN using the XDS Emulators (tested with the XDS200). please review this support discussion