RM0402 Rev 6 1125/1163
RM0402 Debug support (DBG)
1153
Figure 360. SWJ debug port
Figure 360 shows that the asynchronous TRACE output (TRACESWO) is multiplexed with
TDO. This means that the asynchronous trace can only be used with SW-DP, not JTAG-DP.
30.3.1 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
30.4 Pinout and debug port pins
The STM32F412xx MCUs are available in various packages with different numbers of
available pins. As a result, some functionality (ETM) related to pin availability may differ
between packages.
TRACESWO
JTDO
JTDI
NJTRST
nTRST
TDI
TDO
SWJ-DP
TDO
TDI
nTRST
TCK
TMS
nPOTRST
JTAG-DP
nPOTRST
From
power-on
reset
DBGRESETn
DBGDI
DBGDO
DBGDOEN
DBGCLK
SW-DP
SWCLKTCK
SWDOEN
SWDO
SWDITMS
SWD/JTAG
select
JTMS/SWDIO
JTCK/SWCLK
(asynchronous trace)
ai17139
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