Mechanism To Select The Jtag-Dp Or The Sw-Dp; Figure 186. Swj Debug Port - ST STM32F101 Series Reference Manual

Debug support (DBG)

Figure 186. SWJ debug port

JNTRST
JTMS/SWDIO
JTCK/SWCLK
Figure 186
TDO. This means that the asynchronous trace can only be used with SW-DP, not JTAG-DP.
20.3.1

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
470/501
(asynchronous trace)
TRACESWO
SWJ-DP
JTDO TDO
TDI
JTDI
nTRST
SWD/JTAG
SWDITMS
SWDO
SWDOEN
SWCLKTCK
shows that the asynchronous TRACE output (TRACESWO) is multiplexed with
select
TDO
TDI
nTRST
JTAG-DP
TCK
TMS
nPOTRST
nPOTRST
DBGRESETn
DBGDI
DBGDO
SW-DP
DBGDOEN
DBGCLK
RM0008
From
power-on
reset