Universal J-Link Adapter

Quick access links
Adapter v4.0 schematic (PDF) // Adapter v4.0 gerber-files
Basic J-Link Commander usage and using Segger Real-Time Transfer (RTT) (instead of UART) for real-time debugging

This multifunctional adapter board, primarily designed for use with a J-Link debugger (but others which follow the standard 20-pin JTAG/SWD pinout also work), allows the user to have the standard 9 pin Cortex-M SWD/JTAG pinout on both a 0.1" (2.54mm) and 0.05" (1.27mm) male pinheader. With additional jumpers it is possible to have extra functionality like UART debugging though the J-Link's VCOM on pins which normally aren't used in some modes, if the probe's hardware supports this. Good labeling of all pin numbers and their corresponding functionality also help to speed-up the embedded-development process. Additional information regarding the pinout of default SWD-headers as well as the voltage output of the J-Link debugger are also printed on the board, along with the pin-numbers of the 10 pin Tag-Connect header.

Furthermore, the adapter PCB can power the target board through the VTREF connection. For this to work a DC-DC converter or LDO regulator can be plugged into the female 3-pin socket on the adapter board to allow the J-Link's 5V-Supply to be converted to, for example 3.3V. Various 3-pin voltage conversion boards are supported due to solder-jumpers available on the back of the adapter, allowing for the VOUTand GNDpins to be swapped around. The 5V voltage can also be supplied as-is on a header pin by changing a jumper position.

Finally a physical reset button (with optional 100 Ω series-resistor and 100 nF filter capacitor) can be used to manually pull the reset line low, even if no debugger is connected. This eliminates the need to add a reset button to the target board and thus saves valuable board space.

The 0.05" (1.27mm) header is recommended for when the target board is mostly connected to the debugger and the board in question also has a header of this size. The 0.1" (2.54mm) IDC header is recommended for use with either regular jumper-wires or a 10 pin Tag-Connect adapter cable. The latter allows target boards to be programmed without having to need a dedicated programming connector mounted, and thus saves on cost.

The figure on the left depicts the TagConnect 2050 (no-legs) cable on the top-right, next to its corresponding footprint. Below this is a 0.05" header with its corresponding cable.

0 - Table of Contents

• Universal J-Link Adapter
  • 0 - Table of Contents
  • 1 - Adapter functionality
    • 1.1 - Supply power to the target board (5V and/or other voltages)
    • 1.2 - Additional functionality on "unused" pins using jumpers (and corresponding tips and tricks)
  • 2 - Serial flashing
  • 3 - Layout guidelines for target boards
  • 4 - BOM
  • 5 - KiCad debug header symbols

1 - Adapter functionality

Aside from the ability to easily make connections to target boards using the well-labeled pinout and corresponding functionality of both output-headers, the following paragraphs give more information regarding additional features this adapter can provide.

📝 Note: The pinout silkscreen has the following syntax:

• ... | ...: The same (J-Link debugger) pin has different SWD or JTAG functionality
• ... / ...: A jumper can be used to route one or the other signal to this pin
• (...): This pin-signal deviates from the default SWD or JTAG pinout

1.1 - Supply power to the target board (5V and/or other voltages)

As previously stated, a DC-DC converter or LDO regulator can be plugged into the 3-pin female header on this adapter with the labels JP1 JP2 5V. This would allow the adapter board to supply power through the VTREF-line (PIN 1) to the target board with the correct voltage, derived from the 5V supply of the J-Link debugger. The 5V voltage can also be made available as-is on PIN 5 of the output headers, by placing a jumper in the correct position of the header labeled GND 5 5V. With the same jumper GND can also be made available on PIN 5. Both the voltage-converter socket and PIN 5-jumper are depicted on the figure on the left.

If the user wishes to not power the target board using VTREF, for example in case of it already receiving power from a battery or external supply, the voltage converter should simply not be plugged in. The J-Link debugger will still receive the correct I/O voltage as a logic-level reference if the MCU's supply voltage is present on VTREF (PIN 1).

If the pinout of the 3-pin voltage converter doesn't match VIN - VOUT - GND, the last two pins can be changed around by swapping the solder joints on JP1 and JP2 on the bottom of the PCB. This is also also depicted on the figure on the left. If the present copper traces are cut on both jumpers and new solder connections are made on the opposite side, the pinout VIN - GND - VOUT will be selected.

The 5V output needs to be enabled on the J-Link using the J-Link Commander software (JLink.exe/JLinkExe). The following command needs to be executed for the 5V supply to be always enabled:

Power On perm

If the target board is powered via a voltage-converter on the adapter PCB, a jumper labeled VTREF 1 below the 0.1" header allows for a current meter to be inserted between the converter and target board. This way its power usage can be monitored, for example in case the J-Link probe doesn't have this functionality build-in. If 5V is supplied to the target board through PIN 5, a jumper in this location can also be substituted for a current meter. Both headers are depicted on the figure on the right.

1.2 - Additional functionality on "unused" pins using jumpers (and corresponding tips and tricks)

In addition to the default SWD or JTAG pinouts it is also possible to add extra functionality to normally unused pins of the 02x05 headers:

• 📌 PIN 5 is normally connected to GND.
  • On the Segger 10 pin Needle Adapter this pin outputs the J-Link's 5V-Supply. A jumper on the adapter board can be used to select this, which was already mentioned in the previous section.
  • 💡 TIP: See the following section to use this pin for serial programming.
• 📌 PIN 6 is normally used for the SWO or TDO connection. A jumper labeled SWO TDO 6, which can be seen on the figure on the right, can however be used to disconnect the debugger from the target board.
  • 💡 TIP: Disconnecting the pin from the debugger can enable the MCU's output pin to be used as a GPIO debug signal. It can for example be set high if some code is running, and low when this is not the case. Simply remove the jumper and add a jumper-wire on the pin labeled 6.
• 📌 PIN 7 is on the standard 9-pin Cortex-M SWD/JTAG pinout not populated since this is the key.
  • SWD mode: A jumper labeled RTCK 7 JL.RX can be used to connect this pin to the J-Link's VCOM RX pin. This way UART debugging can be used in conjunction with SWD.
    • 💡 TIP: The jumper can also be removed, and a separate UART TXD signal from a target board can be connected to the J-Link's RX input by connecting a jumper-wire to the JL.RX pin.
    • 📝 NOTE: It is possible VCOM needs to be enabled on the probe. This can be done using J-Link Commander (JLinkExe/JLink.exe) by executing the following command (VCOM will start working after the next power-cycle):

      VCOM enable

  • JTAG mode: The same jumper can also be used to connect this pin to RTCK if necessary.
• 📌 PIN 8
  • SWD mode: Normally this pin is not connected, but a jumper labeled JL.TX TDI 8 allows it to be connected to the J-Link's VCOM TX pin.
    • 💡 TIP: The jumper can also be removed, and a separate UART RXD signal from a target board can be connected to the J-Link's TX output by connecting a jumper-wire to the JL.TX pin.
  • JTAG mode: On Segger's 9 pin and 19 pin Cortex-M adapters PIN 9 is connected to TDI.
    • 💡 TIP: The TDI signal of a J-Link debugger can be set low or high using J-Link Commander by executing TDI0 and TDI1 respectively, even if there is no target connection active. This signal can thus be used as a GP(I)O line to, for example, an MCU input pin.
  • 📝 NOTE: JL.TX and TDI are for both modes located on the same physical J-Link pin. This means the jumper should normally not need to be disconnected when using the adapter in one or the other mode.
• 📌 PIN 9
  • SWD mode: Normally this pin is not connected. Sometimes a target board however uses this pin as GNDdetect, so it can (as the name implies) detect the presence of a debugger. With a jumper labeled nTRST 9 GND this pin can be connected to GND to enable this functionality.
    • 💡 TIP: When PIN 9 is connected to a microcontroller pin which can act as an output, the adapter can be used to break-out this pin to another instrument for, for example, code-timing analysis. Simply remove the jumper and add a jumper-wire on the pin labeled 9.
  • JTAG mode: On Segger's 9 pin and 19 pin Cortex-M adapters this pin can be connected to nTRST using a solder jumper. On this adapter board this can be done using a regular jumper.
    • 💡 TIP: The nTRST signal of a J-Link debugger can be set low or high using J-Link Commander by executing TRST0 and TRST1 respectively, even if there is no target connection active. This signal can thus be used as a GP(I)O line to, for example, an MCU input pin.
• 📌 PIN 10 is used to reset the target board. A jumper is present to disconnect this line if necessary.
  • 💡 TIP: The nRESET signal of a J-Link debugger can be set low or high using J-Link Commander by executing R0 and R1 respectively, even if there is no target connection active.
    
  • An nRESET button is also present on the adapter board to manually pull the reset line low. An optional (100 Ω) series-resistor R1 and (100 nF) filter capacitor C1 can be mounted on the bottom of the board, both in the 0603 package. They are depicted on the figure on the right. To activate the functionality of R1 jumper JP10 has to be cut.

💡 TIP: ShowHWStatus or ST can be executed in J-Link Commander to show the current VTREF voltage as well as the signal-level of the SWCLK|TCK, TDI, SWO|TDO, SWDIO|TMS, nRESET (TRES) and nTRST pins, even if there is no target connection active.

Additionally a two-pin GND header, next to the JL.TX TDI 8 jumper, also facilitates some additional ground-wire connections for general debug connections.

2 - Serial flashing

Due to the availability of the jumpers on the adapter PCB certain pins can also be used to detect if a target board is plugged in. A board such as the Macropedal can for example be used to check if pin 5 is, via a target board, connected to ground. If this is the case, the Macropedal can enter a command in a terminal to flash firmware to a board. This way one after the other board can be programmed in a series production scenario. The target board can even be powered by the adapter itself for a complete stand-alone setup. The figure on the right depicts such an arrangement. Refer to Segger J-Link debugging tips & tricks - 2 - Scripting for more information.

3 - Layout guidelines for target boards

It is advised to add the following passives to the target board for protection and stability. This is also mentioned on the adapter schematic.

• 10 kΩ pullup on SWDIO|TMS, TDO and TDI (and the target board's RXD line)
• 10 kΩ pulldown on SWCLK|TCK
• 33 to 100 Ω in-line current-limiting resistors on TXD and RXD lines
  • This can be important for when UART is available on a (0.1") external header, and is less important if this is made available on the SWD-header. 100 pF capacitors (after the series resistors) can also help with some filtering and ESD mitigation.

4 - BOM

Component	Footprint	Manufacturer Partnumber	Ordering
J1	02x10 0.1" (2.54mm) Right Angle Keyed Female IDC Socket	Sullins SFH11-PBPC-D10-RA-BK	digikey.be
J2	02x05 0.1" Male Key-Shrouded IDC Header	Samtec TST-105-01-L-D	digikey.be
J3	02x05 0.05" (1.27mm) Male Key-Shrouded Header	Samtec FTSH-105-01-L-D-K	digikey.be
J4	01x03 0.1" Female IDC Socket	Samtec SSW-103-01-G-S	digikey.be
J5, JP4, JP5, JP8, JP9	01x02 0.1" Male IDC Header	Samtec TSW-102-07-L-S	digikey.be
JP3, JP6, JP7	01x03 0.1" Male IDC Header	Samtec TSW-103-07-L-S	digikey.be
SW1	6.5mm Pitch Through-hole Switch	C&K PTS636SL43 LFS	digikey.be
R1	100 Ω 0603 1% (1 kΩ should also work)	Yageo RC0603FR-07100RL	digikey.be
C1	100 nF 0603 10% 50V X7R	Yageo CC0603KRX7R9BB104	digikey.be
	2.54mm Pitch Jumpers	Samtec SNT-100-BK-G	digikey.be
	02x05 0.05" IDC Cable, 6 inch (15 cm) Long	Samtec FFSD-05-D-06.00-01-N	digikey.be
	TagConnect 10 pin IDC to Needles Without Legs (...-NL)	TagConnect TC-2050-IDC-NL	digikey.be
	TagConnect 10 pin IDC to Needles	TagConnect TC-2050-IDC	digikey.be

5 - KiCad debug header symbols

On the repository brechtve-kicad-things symbols are available where the additional functionality, selectable using the jumpers, is depicted for both SWD and JTAG modes. The regular pinouts are put into brackets. The symbols can be found in the library BrechtVE_DebugHeader.lib.

The symbols to be linked to a 0.05" (1.27mm) header on the target board are the following:

Symbols are also supplied to be linked to a TagConnect 2050 footprint. The pin numbers and corresponding functions are mostly the same as for the previously mentioned SWD/JTAG connectors, but the direction in which the pins are laid out on the PCB is different. This is reflected in other symbols:

For reference these symbols, along with additional information regarding jumpers and layout guidelines, can be found on the adapter schematic. A lot more information regarding KiCad itself is also available on the repository brechtve-kicad-things.