Adding devices to the scan chain

You can manually add devices to the scan chain, if required. You might want to do this in the following circumstances:

To add a device to the scan chain:

  1. Select the Devices node in the tree diagram.

  2. Click on Add.... The Add Device dialog box is displayed. The following figure shows an example:

    Figure 23. The Add Device dialog box

    The Add Device dialog box

    The devices available depends on your firmware version.


    Device groups shown in light gray indicates that the related devices are not available. These are usually seen when you autoconfigure a CoreSight development platform.

  3. If the device appears in the list of registered devices:

    1. Select Registered Devices. A registered device is a one that the debug hardware unit can identify and for which some level of debug support exists. That is, a template exists for the device.

    2. Expand the relevant device group.

    3. Select the device that you want to add.

    4. Click on Add. The device is added to the scan chain.


      You can also add a device to the scan chain by double-clicking the device.

    5. If you have multiple devices, repeat steps 4b to 4d to add each registered device.

    6. After you have added all your devices, continue at step 6.

  4. You might want to add a device that is not identified by the debug hardware, because it is a device your are currently developing. To do this:

    1. Select Custom Device.

    2. Enter the name of the device in the Device Name field. This is used as the name of the device node in the tree view, and can have any value.

    3. Enter the JTAG Instruction Register length (in bits) in the IR Length field.


      If you enter an incorrect value for the IR length, any connections that you attempt to make to the device result in failure.

    4. Click on Add. The device is added to the scan chain.

    5. If you have multiple devices, repeat steps 5b to 5d to add each custom device.


    Be aware that you cannot debug a custom device. However, adding the custom device in the correct order and with the correct length enables you to debug the supported devices in the same scan chain.

  5. When you have finished, click Close.


You can remove devices, or change their order in the scan chain, without first having to close the Add Device dialog box.

The following figure shows a number of devices that have been added to the scan chain in a hierarchical manner:

Figure 24. Scan chain devices with tooltip feature displayed

Scan chain devices with tooltip feature displayed

Show/hideConsiderations when adding devices to a scan chain

Be aware of the following:

  • In a traditional JTAG configuration you must add devices in the correct order. The device nearest to TDO is last on the chain.


    If you add the devices in the wrong order, you can later change the order.

  • In a CoreSight configuration, you must first add the ARMCS-DP device. You can then add the remaining CoreSight devices in any order.

  • Hierarchies are created automatically when a device is added as a CoreSight component, and enables you to manage component interactions easily.

  • The scan chain shows a unique association name for the device, if one exists, to help you to identify the correct device when you are creating associations.

  • When the cursor is placed over a device, a tooltip displays details relating to that device.


    The Associations item in the tooltip only appears if an association has been set up for that device.

Show/hideSee also

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