J-Link / J-Trace User Guide (UM08001) - Microcontrollers

92 CHAPTER 5 Working with J-Link and J-Trace
5.3 JTAG interface
By default, only one ARM device is assumed to be in the JTAG scan chain. If you have
multiple devices in the scan chain, you must properly configure it. To do so, you have
to specify the exact position of the ARM device that should be addressed. Configuration of
the scan is done by the target application. A target application can be a debugger
such as the IAR C-SPY® debugger, ARM’s AXD using RDI, a flash programming application
such as SEGGER’s J-Flash, or any other application using J-Link / J-Trace. It is
the application’s responsibility to supply a way to configure the scan chain. Most
applications offer a dialog box for this purpose.
5.3.1 Multiple devices in the scan chain
J-Link / J-Trace can handle multiple devices in the scan chain. This applies to hardware
where multiple chips are connected to the same JTAG connector. As can be seen
in the following figure, the TCK and TMS lines of all JTAG device are connected, while
the TDI and TDO lines form a bus.
Currently, up to 8 devices in the scan chain are supported. One or more of these
devices can be ARM cores; the other devices can be of any other type but need to
comply with the JTAG standard.
5.3.1.1 Configuration
TDI Device 1 TDO TDI Device 0 TDO
TCK
TMS
TRST
TDI TDO
JTAG
The configuration of the scan chain depends on the application used. Read JTAG
interface on page 92 for further instructions and configuration examples.
5.3.2 Sample configuration dialog boxes
TCK
As explained before, it is responsibility of the application to allow the user to configure
the scan chain. This is typically done in a dialog box; some sample dialog boxes
are shown below.
J-Link / J-Trace (UM08001) © 2004-2010 SEGGER Microcontroller GmbH & Co. KG
TMS
TRST
TCK
TMS
TRST