JTAG Interface Connection (20 pin)
J-Link and J-Trace have a JTAG connector compatible to ARM's Multi-ICE. The JTAG connector is a 20 way Insulation Displacement Connector (IDC) keyed box header (2.54mm male) that mates with IDC sockets mounted on a ribbon cable.
The following table lists the J-Link / J-Trace JTAG pinout:
| Pin | Signal | Type | Description |
|---|---|---|---|
| 1 | VTref | Input | This is the target reference voltage. It is used to check if the target has power, to create the logic-level reference for the input comparators and to control the output logic levels to the target. It is normally fed from Vdd of the target board and must not have a series resistor. |
| 2 | Not connected | NC | This pin is not connected in J-Link. It is reserved for compatibility with other equipment. Connect to Vdd or leave open in target system. |
| 3 | nTRST | Output | JTAG Reset. Output from J-Link to the Reset signal of the target JTAG port. Typically connected to nTRST of the target CPU. This pin is normally pulled HIGH on the target to avoid unintentional resets when there is no connection. |
| 5 | TDI | Output | JTAG data input of target CPU. It is recommended that this pin is pulled to a defined state on the target board. Typically connected to TDI of target CPU. |
| 7 | TMS | Output | JTAG mode set input of target CPU. This pin should be pulled up on the target. Typically connected to TMS of target CPU. |
| 9 | TCK | Output | JTAG clock signal to target CPU. It is recommended that this pin is pulled to a defined state of the target board. Typically connected to TCK of target CPU. |
| 11 | RTCK | Input | Return test clock signal from the target. Some targets must synchronize the JTAG inputs to internal clocks. To assist in meeting this requirement, you can use a returned, and retimed, TCK to dynamically control the TCK rate. J-Link supports adaptive clocking, which waits for TCK changes to be echoed correctly before making further changes. Connect to RTCK if available, otherwise to GND. |
| 13 | TDO | Input | JTAG data output from target CPU. Typically connected to TDO of target CPU. |
| 15 | nRESET | I/O | Target CPU reset signal. Typically connected to the RESET pin of the target CPU, which is typically called "nRST", "nRESET" or "RESET". This signal is an active low signal. |
| 17 | DBGRQ | NC | This pin is not connected inside J-Link. It is reserved for compatibility with other equipment to be used as a debug request signal to the target system. Typically connected to DBGRQ if available, otherwise left open. |
| 19 | 5V-Supply | Output | This pin can be used to supply power to the target hardware. |
Notes
All pins marked NC are not connected inside J-Link. Any signal can be applied here; J-Link will simply ignore such a signal. Pins 4, 6, 8, 10, 12, 14, 16, 18, 20 are GND pins connected to GND in J-Link. They should also be connected to GND in the target system.
Pin 2 is not connected inside J-Link. A lot of targets have pin 1 and pin 2 connected. Some targets use pin 2 instead of pin 1 to supply VCC. These targets will not work with J-Link, unless Pin 1 and Pin 2 are connected on the target's JTAG connector.
Pin 3 (TRST) should be connected to target CPUs TRST pin (sometimes called NTRST). J-Link will also work if this pin is not connected, but you may experience some limitations when debugging. TRST should be separate from the CPU Reset (pin 15)
Pin 11 (RTCK) should be connected to RTCK if available, otherwise to GND.
Pin 19 (5V-Target supply) of the connector can be used to supply power to the target hardware. Supply voltage is 5V, max. current is 300mA. The output current is monitored and protected against overload and short-circuit.
SWD and SWO (also called SWV) Compatibility
SWD Overview
The J-Link and J-Trace support ARMs Serial Wire Debug (SWD). SWD replaces the 5-pin JTAG port with a clock (SWDCLK) and a single bi-directional data pin (SWDIO), providing all the normal JTAG debug and test functionality. SWDIO and SWCLK are overlaid on the TMS and TCK pins. In order to communicate with a SWD device, J-Link sends out data on SWDIO, synchronous to the SWCLK. With every rising edge of SWCLK, one bit of data is transmitted or received on the SWDIO. The data read from SWDIO can than be retrieved from the input buffer.
SWD Connector Pinout
The J-Link and J-Trace JTAG connector is also compatible to ARM's Serial Wire Debug (SWD).
The following table lists the J-Link / J-Trace SWD pinout.
| Pin | Signal | Type | Description |
|---|---|---|---|
| 1 | VTref | Input | This is the target reference voltage. It is used to check if the target has power, to create the logic-level reference for the input comparators and to control the output logic levels to the target. It is normally fed from Vdd of the target board and must not have a series resistor. |
| 2 | Vsupply | NC | This pin is not connected in J-Link. It is reserved for compatibility with other equipment. Connect to Vdd or leave open in target system. |
| 3 | Not used | NC | This pin is not used by J-Link. If the device may also be accessed via JTAG, this pin may be connected to nTRST, otherwise leave open. |
| 5 | Not used | NC | This pin is not used by J-Link. If the device may also be accessed via JTAG, this pin may be connected to TDI, otherwise leave open. |
| 7 | SWDIO | I/O | Single bi-directional data pin. |
| 9 | SWCLK | Output | Clock signal to target CPU. It is recommended that this pin is pulled to a defined state of the target board. Typically connected to TCK of target CPU. |
| 11 | Not used | NC | This pin is not used by J-Link. This pin is not used by J-Link when operating in SWD mode. If the device may also be accessed via JTAG, this pin may be connected to RTCK, otherwise leave open. |
| 13 | SWO | Input | Serial Wire Output trace port. (Optional, not required for SWD communication.) |
| 15 | nRESET | I/O | Target CPU reset signal. Typically connected to the RESET pin of the target CPU, which is typically called "nRST", "nRESET" or "RESET". This signal is an active low signal. |
| 17 | Not used | NC | This pin is not connected in J-Link. |
| 19 | 5V-Supply | Output | This pin is used to supply power to some eval boards. |
Pins 4, 6, 8, 10, 12, 14, 16, 18, 20 are GND pins connected to GND in J-Link. They should also be connected to GND in the target system.
Serial Wire Output (SWO) Overview
J-Link can be used with devices that support Serial Wire Output (SWO). Serial Wire Output (SWO) support means support for a single pin output signal from the core.
Serial Wire Viewer (SWV) Overview
The Instrumentation Trace Macrocell (ITM) and Serial Wire Output (SWO) can be used to form a Serial Wire Viewer (SWV). The Serial Wire Viewer provides a low-cost method of obtaining information from inside the MCU. The SWO can output trace data in two output formats, but only one output mechanism may be selected at any time. The 2 defined encodings are UART and Manchester. J-Link expects UART encoding. Serial Wire Viewer uses the SWO pin to transmit different packets for different types of information. The three sources which can output information via this pin are:
- Instrumentation Trace Macrocell (ITM) for application-driven trace source that supports printf-style debugging. It supports 32 different channels, which allow it to be used for other purposes such as real-time kernel information as well.
- Data Watchpoint and Trace (DWT) for real-time variable monitoring and PC-sampling, which can in turn be used to periodically output the PC or various CPU-internal counters, which can be used to obtain profiling information from the target.
- Timestamping. Timestamps are emitted relative to packets.