AN4467 datasheet(25/33 Pages) STMICROELECTRONICS

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AN4467

Debug management

4.4.1

SWD pin assignment

After reset (SYSRESETn or PORESETn), the pins used for the SWD are assigned as

dedicated pins which are immediately usable by the debugger host.

However, the MCU offers the possibility to disable the SWD, therefore releasing the

associated pins for general-purpose I/O (GPIO) usage. For more details on how to disable

SWD port, refer to the section on I/O pin alternate function multiplexer and mapping of

reference manuals RM0367/ 0376 / 0377.

4.4.2

Internal pull-up and pull-down on SWD pins

Once the SWD 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:

•

SWDIO: alternate function pull-up

•

SWCLK: alternate function pull-down

Having embedded pull-up and pull-down resistors removes the need to add external

resistors.

4.4.3

SWD port connection with standard SWD connector

Figure 13 shows the connection between the STM32L0xx and a standard SWD connector.

Figure 13. SWD port connection

AN4467 Datasheet(PDF) 25 Page - STMicroelectronics