JTAG High Voltage Isolation Board

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Introduction

The  isolation board supports JTAG or SWD+UART isolation. It features a built‑in isolated power supply to power the target side, with selectable 3.3 V / 5 V output via the on‑board DIP switch.
It provides isolation voltage up to 5000 Vrms. Equipped with a standard 20‑pin JTAG connector, this board can be directly connected to J‑LINK and ST‑Link debug probes, and is compatible with most commercial versions of J‑LINK and ST‑Link.
The isolation board has two DIP switches:
  • Debug‑probe‑side DIP switch: Enables/disables power supply via Pin 19. (Marked on PCB: 1 = Pin 19 connected; 3 = Pin 19 disconnected)
  • Target‑side DIP switch: Sets the board output level to 3.3 V or 5 V. (Silkscreen marking is printed on the rear side of the isolation board)

Operating Instructions

  1. Ensure Pin 1 or Pin 19 of your debug probe outputs voltage to supply power to the isolation board. (See detailed configuration below.)
  2. Set the DIP switch to 3.3 V or 5 V according to your target‑board operating voltage. Match the isolation‑board output voltage to the target‑board voltage.
  3. Plug the isolation board directly into the standard 20‑pin JTAG header of the debug probe. Two LEDs should light up. If both LEDs are not illuminated, troubleshoot the voltage output from the debug probe.
  4. Connect your target board to the target‑side connector of the isolation board, then proceed with debugging and firmware downloading.

Debug‑Probe‑Side Voltage Configuration

One DIP switch on the probe side of the isolation board selects whether Pin 19 is used for power supply.

When using ST‑Link

ST‑Link typically outputs 3.3 V from Pin 19 by default. Set the isolation‑board probe‑side DIP switch to position 1 so that ST‑Link can power the isolation board.

When using J‑LINK

Multiple J‑LINK hardware revisions exist with different power‑supply schemes:
  • Most J‑LINK units have on‑board jumpers to enable 3.3 V output on Pin 1. Set the isolation‑board DIP switch to position 3 to disconnect Pin 19 power.
  • If Pin 1 of your J‑LINK cannot output 3.3 V, open J‑Link Commander and execute command: power on perm to enable 5 V output on Pin 19.

  • Then set the DIP switch to position 1.

Notice: If Pin 1 outputs 3.3 V while Pin 19 outputs 5 V simultaneously, you must set the DIP switch to position 3 to disable power from Pin 19.

Troubleshooting for abnormal operation

  • Confirm both LEDs on the isolation board are lit to verify proper power supply.
  • Check debug signal lines (SWDIO, SWCLK) routed to the MCU on the target board. If series resistors are present on these traces, replace them with 0‑ohm resistors.

 

 

 

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