Does SWDIO need a pullup?
SWD connections The SWDIO, SWCLK and SWO signals are typically pulled up on the target to keep them stable when the debug equipment is not connected. All pull-up resistors must be in the range 1K-100KΩ. The VTREF signal is typically connected directly to the VDD rail.
Does JTAG need pullup resistor?
Although Virtex JTAG ports have internal pull-ups that are connected by default on TDI and TMS, Xilinx suggests using the external pull-ups to ensure that the device does not enter Boundary Scan mode. It is not necessary to place a pull-up resistor on TCK or on the output TDO; they can be left floating.
Which register is used to enable or disable the internal pull-up resistor for input pins?
PORTx register
Now the corresponding bits in PORTx register can be used to enable/disable pull-up resistors associated with that pin.To enable pull-up resistor, set bit in PORTx to 1, and to disable set it to 0….GPIO Registers.
| Register | Description |
|---|---|
| PINx | Used to Read the data from the port pins |
Why do we use JTAG?
By providing a mechanism to control and monitor all the enabled signals on a device from a four-pin TAP, JTAG significantly reduces the physical access required to test a board. There are two main ways that this boundary scan capability can be used to test a board.
Is the SWDIO pull-up required on the board?
One section of the STM32L431 manual (46.4 Pinout and debug port pins) says: To avoid any uncontrolled I/O levels, the device embeds internal pull-ups and pull-downs on the JTAG input pins: For SWDIO bidirectional management, the line must be pulled-up on the board (100 kOhm recommended by ARM).
What kind of power supply does STM32 board have?
I am starting with a simple STM32 board that has only SWD (i.e., SWDIO, SWCLK, SWO, and NRST) and 3V power supply. (Yes, I have double-checked the connections of all of the above pins, both on the schematic, and with a continuity tester on the actual soldered board.
Is the SWD on stlink V3 not working?
However, it appears that the SWD (or even reading target voltage) is not working. I tried various transport select; here is my openocd.cfg: