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Chaining Multiple Targets

Chaining multiple targets, or target chaining, refers to the ability to attach multiple target systems to one single JTAG bus. In this configuration, ULINKpro can access one target at a time.

The following requirements must be supported by each target device:

  • BYPASS 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.

ULINKpro scans for an IDCODE, a device name, and an IR length for each target, and sets up the targets automatically. Scan results are displayed in the JTAG Device Chain section of the Target Driver Setup dialog.

Device Chaining

If the automatic setup fails, use Manual Configuration to define the device attributes. The target device must support BYPASS register in order to use Manual Configuration. Refer to JTAG Device Chain.

To chain targets:

  • Connect the control signals in parallel (TMS and TCLK).
  • Connect the data signals in series to form a bus (TDO to TDI).

Data output of one target (TDO) should be the input of the next target (TDI) in the chain.

Chaining Targets Diagram


  • Target chaining is possible in JTAG mode only.
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