Chain Devices

Chaining devices, or target chaining, is the ability to connect more target systems to one JTAG bus and to a single debugger adapter. J-Link/J-Trace can reach chained devices, and program the Flash memory, debug, and trace each target individually.

Each device within the chain has to support:

• BYPASSS register.
• The IDCODE instruction must immediately follow a reset of the Test Access Port (TAP).
• Bit 0 of ID Code must be 1.
• In CAPTURE-IR state, the fixed value 1 must be loaded into the IR.

J-Link/J-Trace scans for the target IDCODE, device name, and IR length, and sets up the targets automatically. The scan results are shown in the JTAG Device Chain section of the Target Driver Setup dialog (Project — Options for Target — Debug — Settings).

To chain devices:

• Connect the control signals in parallel (TMS and TCLK) .
• Connect the data signals in series to form a bus (TDO to TDI).
• A maximum of 8 chained devices are supported.