DocID023035 Rev 4

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AN4080

Debug management

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4.3.2

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 RM0091 section on I/O pin alternate function multiplexer and

mapping.

4.3.3

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.

4.3.4

SWD port connection with standard SWD connector

Figure 9 shows the connection between the STM32F0xx and a standard SWD connector.

Figure 9. SWD port connection

Caution:

In STM32F07x/04x devices, the SWCLK and SWDIO pins are supplied by the VDDIO2

domain. Therefore, you must provide VDDIO2 supply instead of VDD to the SWD connector

in order to ensure correct behavior of the debugger tool.