Target Interface SWD

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ARM's Serial Wire Debug (SWD) replaces the traditional 5-pin JTAG debug interface by introducing a 2-pin interface with a clock (SWDCLK) and a single bi-directional data pin (SWDIO), providing all the normal JTAG debug and test functionality, anyhow dayisy-chaining devices as via JTAG is not possible. SWDIO and SWCLK are overlaid on the TMS and TCK pins, allowing to use the same connector for JTAG and SWD. In order to communicate with a device via SWD, data is send on SWDIO, synchronous to the SWCLK. With every rising edge of SWCLK, one bit of data is transmitted or received on the SWDIO pin.

SWO

In addition to the debug signals, the SWD interface also specifies a dedicated pin which allows the target CPU to output specific data like printf output on a dedicates pin via UART or Manchester protocol. This pin is unidirectional, so it is not possible to send data to the target CPU on this pin.

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