Debug support (DBG) RM0091
720/742 Doc ID 018940 Rev 1
29.3.1 SW debug port pins
Two pins are used as outputs for the SW-DP as alternate functions of general purpose I/Os.
These pins are available on all packages.
29.3.2 Flexible SW-DP pin assignment
After reset (SYSRESETn or PORESETn), the pins used for the SW-DP are assigned as
dedicated pins which are immediately usable by the debugger host.
However, the MCU offers the possibility of disabling all or part of the SW-DP port and can
then release the associated pins for general-purpose I/O (GPIO) usage. For more details on
how to disable SW-DP port pins, please refer to sectionSection 8.3.2: I/O pin alternate
function multiplexer and mapping on page 121.
29.3.3 Internal pull-up & pull-down on SW pins
The microncontroller embeds internal pull-up & pull-down resistors on the SW input pins:
● SWDAT: internal pull-up
● SWCLK: internal pull-down
Once the SW I/O is released by the user software, the GPIO controller takes control of these
pins. The reset states of the GPIO control registers put the I/Os in the equivalent states:
● SWDAT: input pull-up
● SWCLK: input pull-down
Having embedded pull-up and pull-down resistors removes the need to add external
resistors.
29.4 ID codes and locking mechanism
There are several ID codes inside the MCU. ST strongly recommends the tool
manufacturers (Keil, IAR, Raisonance, ...) to lock their debugger using the MCU device ID
located at address 0x40015800.
Only the DEV_ID(15:0) should be used for identification by the debugger/programmer tools
(the revision ID must not be taken into account).
Table 107. SW debug port pins
SW-DP pin name
SW debug port
Pin
assignment
Type Debug assignment
SWDIO IO Serial Wire Data Input/Output PA13
SWCLK I Serial Wire Clock PA14
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