Configuring CoreSight systems with multiple devices per JTAG-AP multiplexor port

The debug hardware unit does not support auto-detection of devices behind a JTAG-AP. Therefore, you must manually specify the JTAG scan chain attributes so that the unit can put the other devices into BYPASS.

To debug CoreSight systems that have processors connected to the Debug Access Port (DAP) through JTAG-AP, debug hardware must know the pre-bits and post-bits for JTAG operations. The following figure shows a hypothetical scan chain that could be connected to a JTAG-AP.

Figure 51. Scan chain connected to a JTAG-AP

To view this graphic, your browser must support the SVG format. Either install a browser with native support, or install an appropriate plugin such as Adobe SVG Viewer.


Multiple devices on the scan chain are connected in series, with data flowing serially from TDI to TDO. This means that debugging a given target in the chain requires that certain pre-scan and post-scan bits are used to ensure that the other devices are not affected by the data directed at the target device, and that the data is positioned correctly in the serial scan for the target device.

To debug this system, you must set the following four configuration items:

Show/hideSee also

Copyright © 2010-2011 ARM. All rights reserved.ARM DUI 0498D
Non-ConfidentialID071311