STLINK-V3MODS – Bridge GPIOs won’t work as Outputs

[CBier.1]

Hi everyone,

I’m trying to use the STLINK-V3MODS Bridge GPIOs (GPIO0–GPIO3) as digital outputs, but none of them show any voltage change at the pins — not even in Open-Drain mode with an external pull-up.

All API calls (InitGPIO / SetResetGPIO / ReadGPIO) report BRG_NO_ERR,
but on the hardware side, the GPIO pins stay flat at 0 V regardless of the configuration or the logical state set.

🧩 Setup

• Probe: STLINK-V3MODS 

• OS: Windows 10/11, Visual Studio x64

• DLL: STLinkUSBDriver.dll in the same folder

• Using official STLINK-V3 Bridge API from ST:
  :backhand_index_pointing_right: STLINK-V3 Bridge Software Package (stlink-v3-bridge-v1-2-0.zip)
  (contains bridge.h, bridge.cpp, and example project apiBridgeProject)

:gear: What I did

• Used InitGPIO() + SetResetGPIO()

• Tried both Push-Pull and Open-Drain modes

• T_VCC is connected (3.3 V detected)

• Closed all COMs between runs (CloseBridge(COM_UNDEF_ALL))

Result:

• Software side → success (BRG_NO_ERR, errMask = 0x00)

• Hardware side → no voltage change, always 0 V

• Tried with LED + 1 kΩ to 3.3 V, tried external 10 kΩ pull-up — no visible switching

It looks like the Bridge GPIOs are either disabled in firmware, or blocked by the internal level-shifters.

:question_mark: Questions to ST / community

1. Are Bridge GPIOs on STLINK-V3MODS truly open-drain only (through level-shifters)?

2. Has anyone measured an actual sourcing HIGH at CN2 pins in Push-Pull mode?

3. Any official documentation (UM/AppNote) confirming this hardware behavior?

[AScha.3]

Hi,

i never played with the bridge on V3mods, but from bridge.cpp :

// GPIO 0, 1, 2, 3 config, Bit1-0 mode, Bit3-2 speed, Bit5-4 pull, Bit6 output type

and xx.h :

/// GPIO port mode configuration, see also \ref LIMITATION
typedef enum {
	GPIO_MODE_INPUT = 0,  ///< Input mode
	GPIO_MODE_OUTPUT = 1, ///< Ouptput mode
	GPIO_MODE_ANALOG = 3  ///< Analog mode
}Brg_GpioModeT;

/// GPIO port output speed configuration
typedef enum {
	GPIO_SPEED_LOW = 0,      ///< Low speed
	GPIO_SPEED_MEDIUM = 1,   ///< Medium speed
	GPIO_SPEED_HIGH = 2,     ///< High speed
	GPIO_SPEED_VERY_HIGH = 3 ///< Very high speed
}Brg_GpioSpeedT;

/// GPIO port pull-up/pull-down configuration
typedef enum {
	GPIO_NO_PULL = 0,  ///< No pull-up, no pull-down
	GPIO_PULL_UP = 1,  ///< Pull-up
	GPIO_PULL_DOWN = 2 ///< Pull-down
}Brg_GpioPullT;

/// GPIO port output type configuration
typedef enum {
	GPIO_OUTPUT_PUSHPULL = 0, ///< Output push-pull
	GPIO_OUTPUT_OPENDRAIN = 1 ///< Output open-drain
}Brg_GpioOutputT;

/// GPIO init configuration, see also \ref LIMITATION
typedef struct {
	Brg_GpioModeT Mode;         ///< GPIO port mode
	Brg_GpioSpeedT Speed;       ///< GPIO port output speed
	Brg_GpioPullT Pull;         ///< GPIO port pull-up/pull-down
	Brg_GpioOutputT OutputType; ///< GPIO port output type
}Brg_GpioConfT;

/// GPIO init parameters for Brg::InitGPIO(), see also \ref LIMITATION
typedef struct {
	uint8_t GpioMask; ///< GPIO(s) to be configured (one or several value of #Brg_GpioMaskT)
	uint8_t ConfigNb; ///< Number of #Brg_GpioConfT pointed by pGpioConf:\n
	                  ///< must be #BRG_GPIO_MAX_NB or 1 (if 1 pGpioConf[0] used for all gpios)
	Brg_GpioConfT *pGpioConf;  ///< Table of ConfigNb init configuration.\n
	                  ///< If #BRG_GPIO_MAX_NB, pGpioConf[0] for GPIO_0, .., pGpioConf[3] for GPIO_3. \n
	                  ///< GPIO(s) that are not present in GpioMask are not configured.
} Brg_GpioInitT;

..so pins can be set to in, out, pull..  like any standard i/o pin, depending on : const Brg_GpioInitT *pInitParams .

What you set here ?