What is the JTAG Interface?
Visually, the JTAG interface is the blue 20-pin connector shown in the image above.
What is the Purpose of the JTAG Interface?
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To download programs to the microcontroller.
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To debug the microcontroller online, such as step debugging, power-off debugging, viewing register values, etc.
Does the JTAG interface for STM32 need external pull-up or pull-down resistors?
Answer: It can work with or without them. (There is no need to discuss which is correct)
Why can it work without them?
Practical evidence: It can function normally without them.
Theoretical basis: The STM32 reference manual explains this; please refer to the text circled in red in the image below:
JTAG Circuit Diagram:
The JTAG interface is also the SWD interface; JTAG uses 6 pins, while SWD uses 2 pins. (This does not include the power supply pins.)
STM32 supports both JTAG and SWD modes, which can be switched in software as shown in the image below:
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