Various ARM emulator interface diagrams

ULINK2 JTAG/SWD interface

How is the ULINK2 interface defined?
The following is the definition of the ULINK2 interface:

The following is the standard interface arrangement:

ST-Link SWIM & JTAG/SWD interfaces

The following is the standard interface arrangement:


ST-Link specified standard interface 

J-Link JTAG/SWD interface

The following is the standard interface arrangement:

Standard interface specified by J-Link

JTAG pin diagram:

1. Differences between SWD and traditional debugging methods

1. SWD mode is more reliable than JTAG in high-speed mode

2. When one GPIO is missing, you can use SWD emulation, which supports fewer pins.

3. When the size of the board is limited, it is recommended to use SWD mode

2. Emulator support for SWD mode

1. Support of SWD mode by common emulators on the market

JLINKV8 supports SWD simulation mode very well, and the speed can reach 10M

ULINK2 supports SWD mode very well, and the speed can reach 10M

2. Differences in SWD hardware interface

(1) The hardware interfaces required by JLINKV7 are: GND, RST, SWDIO, SWDCLK

(2) The hardware interfaces required by JLINKV8 are: VCC, GND, RST, SWDIO, SWDCLK (Note: Below are my actual connections and corresponding experimental results using JLINKV8)

(3) ULINK1 does not support SWD mode

(4) The hardware interfaces required by ULINK2 are: GND, RST, SWDIO, SWDCLK

3. Setting SWD mode in MDK

Normal JTAG requires 20 pins, while J-Link's SWD only needs 2 wires (PA13/JTMS/SWDIO, PA14/JTCK/SWCLK) (plus the power line, it's 4), which saves 3 I/O ports (PA15/JTDI, PB3/JTDO, PB4/JNTRST) for other use, and can save some board space (only 4 ports are needed)

first step:

Step 2:

In addition, the JTAG pins can be reused as IO ports, but in this case, JLINK cannot connect to the chip. There are two solutions:

    (1) Write another program, do not reuse JTAG as an I/O port, and then write this program into the chip using the serial port tool.

    (2) Set BOOT0/BOOT1 to boot from internal RAM. Then the program in FLASH will not be executed after power-on, so JLINK can successfully "take over" the JTAG pins.

With the launch of the Cortex series by ARM, SWD debugging has become everyone's first choice. SWD is not only comparable in speed to JTAG, but also uses far fewer debugging lines. When debugging with SWD, many people generally use 4 lines:

① VCC - Power supply

② GND - Ground

③ SWDIO - Data

④ SWCLK - Clock

When downloading NXP's LPC1114, both ULINK2 and JLINK V8 are available. However, for STM32, if JLINK V8 is used, the download is possible, but if ULINK2 is used, the download always times out. However, if the NRESET reset line is added, the download is possible. Therefore, in order to be compatible with all chips and debugging tools, it is best to reserve the interface in the following way:

PIN 1: GND  

PIN 2: NRST  

PIN 3: VCC 

PIN 4: SWDIO  

PIN 5: SWDCLK

Of course, sometimes only three lines are needed, but this is unstable for some chips:

PIN 1: GND  

PIN 2: SWDIO  

PIN 3: SWDCLK

So you can also use the following method:

1 - VCC;  

2 - GND;  

3 - SWDCLK;  

4 - SWDIO;  

5 - NRST.  

The three wires in the middle are required, NRST can be added or not. Some people say that VCC can be added to power the output interface chip ALVC164245 of JLink.