How many connections are required for JTAG

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The JTAG interface standard requires the following connections:

  • TDI (Test Data In)
  • TDO (Test Data Out)
  • TCK (Test Clock)
  • TMS (Test Mode Select)

However, when designing your hobby project with a JTAG interface, allocate at least 8 pins on a header (dedicated header is best), for the following signals:

  • TDI
  • TDO
  • TCK
  • TMS
  • TRST (Test Reset)
  • VDD
  • GND
  • DONE

Plus any chip-specific or platform-specific configuration pins. For example, most devices and programmers use the DONE signal to specify that the programming succeeded.