25.3.1 Mechanism to select the JTAG-DP or the SW-DP

By default, the JTAG-Debug Port is active.
If the debugger host wants to switch to the SW-DP, it must provide a dedicated JTAG
sequence on TMS/TCK (respectively mapped to SWDIO and SWCLK) which disables the
JTAG-DP and enables the SW-DP. This way it is possible to activate the SWDP using only
the SWCLK and SWDIO pins.
This sequence is:
1. Send more than 50 TCK cycles with TMS (SWDIO) =1
2. Send the 16-bit sequence on TMS (SWDIO) = 0111100111100111 (MSB transmitted
first)
3. Send more than 50 TCK cycles with TMS (SWDIO) =1

25.3 SWJ debug port (serial wire and JTAG)
The STM32F100xx core integrates the Serial Wire / JTAG Debug Port (SWJ-DP). It is an
ARM standard CoreSight debug port that combines a JTAG-DP (5-pin) interface and a SWDP
(2-pin) interface.
● The JTAG Debug Port (JTAG-DP) provides a 5-pin standard JTAG interface to the AHPAP
port.
● The Serial Wire Debug Port (SW-DP) provides a 2-pin (clock + data) interface to the
AHP-AP port.
In the SWJ-DP, the two JTAG pins of the SW-DP are multiplexed with some of the five JTAG
pins of the JTAG-DP.