---
title: Connector Standards
description: Debug connector pinouts, part numbers, and probe compatibility
sidebar:
  order: 2
---

Debug connectors come in several standard pinouts. Knowing which one your board uses determines what probe and cable you need. This page covers the common standards you will encounter.

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## ARM Cortex Debug Connector (10-pin, 1.27mm)

The most common connector on modern Cortex-M boards. 10 pins, 1.27mm (0.05") pitch, dual-row. Defined by ARM in the CoreSight technical reference.

| Pin | Signal | Pin | Signal |
|-----|--------|-----|--------|
| 1 | VTref | 2 | SWDIO/TMS |
| 3 | GND | 4 | SWCLK/TCK |
| 5 | GND | 6 | SWO/TDO |
| 7 | Key (no pin) | 8 | TDI |
| 9 | GNDDetect | 10 | nRESET |

Notes:

- Pin 7 is keyed (no pin present) to prevent reverse insertion
- Supports both SWD (pins 2, 4, 6, 10) and JTAG (pins 2, 4, 6, 8, 10) on the same connector
- SWO (pin 6) is optional -- used for Serial Wire Output trace data
- VTref (pin 1) is the target voltage reference, not a power supply

Common part numbers:

- **Header**: Samtec FTSH-105-01-F-DV-K (shrouded) or equivalent 2x5 1.27mm
- **Cable**: Samtec FFSD-05-D-xx (flat flex), or standard 10-pin 1.27mm ribbon

---

## Legacy ARM JTAG Connector (20-pin, 2.54mm)

The original ARM debug connector. 20 pins, 2.54mm (0.1") pitch. Still found on older boards, evaluation kits, and FPGA dev boards. Half the pins are GND.

| Pin | Signal | Pin | Signal |
|-----|--------|-----|--------|
| 1 | VTref | 2 | VSupply |
| 3 | nTRST | 4 | GND |
| 5 | TDI | 6 | GND |
| 7 | TMS / SWDIO | 8 | GND |
| 9 | TCK / SWCLK | 10 | GND |
| 11 | RTCK | 12 | GND |
| 13 | TDO / SWO | 14 | GND |
| 15 | nRESET | 16 | GND |
| 17 | DBGRQ | 18 | GND |
| 19 | DBGACK | 20 | GND |

Notes:

- Even-numbered pins (except 2) are all GND -- this provides shielding for the signal lines
- Pin 2 (VSupply) is optional target power
- RTCK (pin 11) is return clock for adaptive clocking -- rarely used on modern targets
- DBGRQ/DBGACK are legacy signals from the ARM7/9 era
- SWD signals are aliased on pins 7, 9, 13 -- a 20-pin connector can carry SWD without an adapter

---

## ARM Cortex Debug+Trace Connector (20-pin, 1.27mm)

Extended version of the 10-pin connector with ETM trace signals. 20 pins, 1.27mm pitch. Used when you need instruction trace capture.

| Pin | Signal | Pin | Signal |
|-----|--------|-----|--------|
| 1 | VTref | 2 | SWDIO/TMS |
| 3 | GND | 4 | SWCLK/TCK |
| 5 | GND | 6 | SWO/TDO |
| 7 | Key (no pin) | 8 | TDI |
| 9 | GNDDetect | 10 | nRESET |
| 11 | GND/Key | 12 | TRACECLK |
| 13 | GND/Key | 14 | TRACEDATA\[0\] |
| 15 | GND | 16 | TRACEDATA\[1\] |
| 17 | GND | 18 | TRACEDATA\[2\] |
| 19 | GND | 20 | TRACEDATA\[3\] |

Notes:

- Pins 1--10 are identical to the 10-pin connector
- Pins 12--20 carry parallel trace data (4-bit wide)
- A 10-pin cable works on a 20-pin header (connects to the first row only)
- mcjtag does not currently support trace capture, but the connector carries SWD/JTAG signals that mcjtag uses

---

## STDC14 (STMicroelectronics 14-pin)

ST's 14-pin connector, found on newer STM32 Nucleo and Discovery boards. 1.27mm pitch.

| Pin | Signal | Pin | Signal |
|-----|--------|-----|--------|
| 1 | NC | 2 | VTref |
| 3 | NC | 4 | SWDIO/TMS |
| 5 | GND | 6 | SWCLK/TCK |
| 7 | GND | 8 | SWO/TDO |
| 9 | Key (no pin) | 10 | TDI |
| 11 | NC | 12 | nRESET |
| 13 | VCP_RX | 14 | VCP_TX |

Notes:

- Pins 2--12 map to the standard ARM 10-pin signals (with offset)
- Pins 13--14 provide a Virtual COM Port (VCP) for UART through the ST-Link -- useful for serial debug output
- Backwards-compatible: a 10-pin cable can mate with pins 2--12 (with a 14-to-10 adapter or careful alignment)

---

## Probe-to-Connector Compatibility

Which probes work with which connectors without adapters:

| Probe | 10-pin (1.27mm) | 20-pin (2.54mm) | 20-pin (1.27mm) | STDC14 |
|-------|:---:|:---:|:---:|:---:|
| DAP-Link | Varies by board | Varies by board | -- | -- |
| ST-Link V2 | -- | Yes (included cable) | -- | -- |
| ST-Link V3 | -- | -- | Yes (STDC14 adapter available) | Yes |
| J-Link | Yes (included adapter) | Yes (included cable) | Yes (adapter) | -- |
| FTDI-based | Depends on breakout board | Depends on breakout board | -- | -- |

Most probes ship with a 20-pin 2.54mm cable. For 10-pin 1.27mm targets, you typically need:

- A 20-to-10 adapter board (Segger, Olimex, and others sell these)
- Or a probe that natively supports 10-pin (J-Link with the needle adapter)

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## Adapter Cables

Common adapters for converting between connector standards:

| From | To | Part / Source |
|------|----|---------------|
| 20-pin 2.54mm | 10-pin 1.27mm | Segger J-Link 20-to-10 adapter, Olimex ARM-JTAG-20-10 |
| 20-pin 2.54mm | 20-pin 1.27mm | Segger 20-pin adapter |
| STDC14 | 10-pin 1.27mm | ST STDC14-to-MIPI10 adapter |

When in doubt, buy a probe that matches your board's connector natively. Adapters add length and potential signal integrity issues at higher clock speeds.

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## Tag-Connect (Pogo Pin)

Tag-Connect is a pogo-pin system that eliminates the need for a permanent header on the target board -- just a pattern of pads and locating holes on the PCB.

| Model | Pins | Pitch | Use Case |
|-------|------|-------|----------|
| TC2030 | 6 | 1.27mm | SWD (minimal) |
| TC2050 | 10 | 1.27mm | Full ARM 10-pin |
| TC2070 | 14/20 | 1.27mm | JTAG with trace |

Tag-Connect comes in two variants:

- **Legged** (TC20xx-NL) -- retaining clips hold the connector against the board hands-free
- **No-leg** (TC20xx) -- you hold it in place manually, useful for quick production checks

Tag-Connect is popular for production programming and space-constrained designs where a permanent header is not practical. The footprint on the PCB is much smaller than a shrouded connector.

For mcjtag use, the cable plugs into your probe's standard connector on one end and presses onto the board's pads on the other.

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## Identifying Your Board's Connector

If you are not sure which connector your board has, check these things:

1. **Count the pins.** 10-pin and 20-pin are most common. If it is 14-pin, it is almost certainly STDC14.
2. **Measure the pitch.** 1.27mm pins are visibly smaller and closer together than 2.54mm.
3. **Look for a key.** Shrouded connectors with a notch or missing pin are keyed to prevent reverse insertion.
4. **Check the board schematic.** The connector is usually labeled in the silkscreen or documentation.

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For wiring details and probe configuration, see [Hardware Setup](/guides/hardware-setup/).
