Isolated CMSIS‑DAP V2 Probe Helps Developers Avoid Ground Damage During Debugging

Many embedded engineers ask the same question when reviewing our schematic for this isolated CMSIS‑DAP V2 probe: why not use a single multi‑channel isolator, or reduce to two isolators to cut BOM cost, instead of three…

Many embedded engineers ask the same question when reviewing our schematic for this isolated CMSIS‑DAP V2 probe: why not use a single multi‑channel isolator, or reduce to two isolators to cut BOM cost, instead of three ADUM1201ARZ? This is not arbitrary overdesign; it is a deliberate design decision built for industrial debug environments, long‑term production stability, and real pain points raised by overseas developers.

Market Reality: The Isolated DAP Confusion

A large number of debug probes labelled “isolated DAP” on the market vary wildly in quality. Many low‑cost units deliver fake isolation: simple resistors, basic optocouplers, or isolated power while leaving debug signals sharing a common ground, which fails to break ground loops. Even some genuine isolated designs compromise by mixing different isolator part numbers, removing the SWO trace channel, or squeezing multiple signals into limited isolation channels.

Those probes may work for slow, simple debugging, but they suffer from frequent SWO packet loss and unstable timing. Mixed part numbers create headaches for stock control and SMT assembly, leading to poor unit‑to‑unit consistency. Overseas engineers working with industrial, high‑voltage and cross‑ground systems often face random lockups or damaged probes/target boards, resulting in high support overhead.

The Tittron / FlykanTech Implementation

Rather than following this race‑to‑the‑bottom cost trend, Tittron reworked this isolated debug probe from the ground up. The goal is a hardware design suitable for stable mass production, trusted by industrial customers worldwide, while retaining the full feature set of CMSIS‑DAP V2. Below is the complete hardware specification.

Product Overview

Industrial fully‑isolated high‑speed debug probe. Supports CMSIS‑DAP V2 (WinUSB Bulk), high‑speed SWO trace and isolated UART. Galvanic isolation is applied to both power and signals to eliminate ground‑loop noise and protect hardware against damage. Designed for mass production and global sales.

Core Bill of Materials

• Main MCU: STM32F401CCU6
• Isolated Power Module: B0505S‑2WR2 (genuine isolated 5 V supply)
• Signal Isolator: ADUM1201ARZ × 3 pcs (single part number for easier manufacturing and reduced risk of direction misplacement)

Six Isolated Signal Assignments (3 × ADUM1201)

Each ADUM1201 carries one forward channel (Probe → Target) and one reverse channel (Target → Probe).

Ref.	Forward (Probe → Target)	Reverse (Target → Probe)	Function
U1	TX	RX	Isolated UART
U2	SWCLK	SWDIO	SWD Debug Bus
U3	nRST	SWO	Reset + High‑Speed Trace

Total: 3 forward + 3 reverse channels, six fully isolated signals.

10‑Pin Standard Debug Connector (2×5, 2.54 mm)

Pin No.	Signal Name	Isolated	Remarks
1	Vtarget	No	Target voltage sensing
2	SWDIO	Yes	Input from target
3	GND	No	Isolated side ground
4	SWCLK	Yes	Output to target
5	GND	No	Isolated side ground
6	nRST	Yes	Output to target
7	SWO	Yes	Trace input from target
8	TX	Yes	UART output to target
9	GND	No	Isolated side ground
10	RX	Yes	UART input from target

Secondary Header (Breadboard Flying Wires)

Single‑row header pins: Vtarget, SWDIO, SWCLK, nRST, SWO, TX, RX, GND

Firmware Requirements

• Firmware: Official DAPLink
• Mode: CMSIS‑DAP V2 (Bulk high‑speed)
• Enabled Features: SWO Trace, CDC Virtual COM Port, mass storage drag‑and‑drop upgrade

Key Advantages for Production & Export

• Only one isolator part number (ADUM1201), simpler inventory and SMT assembly
• ST + ADI reference design, widely recognised by engineers worldwide with low failure rate
• Full six‑channel isolation with dedicated SWO, high‑end CMSIS‑DAP V2 configuration
• Genuine galvanic isolation: independent isolated power plus signal isolation for industrial noise immunity, distinct from cheap pseudo‑isolated probes

Permanent Design Rules (Do NOT Modify)

Locked Design Rules

• Do not mix ADUM1200 / ADUM1202
• Do not remove SWO (core selling point of DAP V2)
• Do not remove the independent isolated power supply