Manually assert RS232 flow control signals

Hello,

I'm working on a project using a STM32L4

I'm using RS232 on the USART1 (with a MAX2328). I'm connecting the RS232 on my computer using a USB adaptator. And I use a RS232 analyzer with LEDs to monitor the flow control signals.

What I would like to do is manually assert DCD, DSR, DTR and RI with GPIOs but when I read the state of one of the pin associed to one of these signals, it's always 0.

This is how I initialize the GPIOs :

//DTR ----> PA8
 GPIO_InitTypeDef DTR;
 if(Config_RSDTR!=DISABLE)
 {
 if(Config_RSDTR==OUTPUT)
 {
 DTR.Alternate = GPIO_MODE_OUTPUT_PP;
 DTR.Mode = GPIO_MODE_OUTPUT_PP ;
 DTR.Pin = GPIO_PIN_8;
 DTR.Pull = GPIO_NOPULL;
 DTR.Speed = GPIO_SPEED_FREQ_LOW;
 HAL_GPIO_Init(GPIOA,&DTR);
 HAL_GPIO_WritePin(GPIOA,GPIO_PIN_8,1);
 }
}
 //DCD ----> PC9
 GPIO_InitTypeDef DCD;
 if(Config_RSDCD!=DISABLE)
 {
 if(Config_RSDCD==INPUT)
 {
 DCD.Pin = GPIO_PIN_9;
 DCD.Mode = GPIO_MODE_INPUT;
 DCD.Pull = GPIO_NOPULL;
 DCD.Speed = GPIO_SPEED_FREQ_LOW;
 DCD.Alternate = GPIO_MODE_INPUT;
 HAL_GPIO_Init(GPIOC, &DCD);
 }
 }
 //DSR -----> PC8
 GPIO_InitTypeDef DSR;
 if(Config_RSDSR!=DISABLE)
 {
 if(Config_RSDSR==INPUT)
 {
 DSR.Pin = GPIO_PIN_8;
 DSR.Mode = GPIO_MODE_INPUT;
 DSR.Pull = GPIO_NOPULL;
 DSR.Speed = GPIO_SPEED_FREQ_LOW;
 DSR.Alternate = GPIO_MODE_INPUT;
 HAL_GPIO_Init(GPIOC, &DSR);
 }
 }
 //RI -----> PC7
 GPIO_InitTypeDef RI;
 if(Config_RSRI!=DISABLE)
 {
 if(Config_RSRI==INPUT)
 {
 RI.Pin = GPIO_PIN_7;
 RI.Mode = GPIO_MODE_INPUT;
 RI.Pull = GPIO_NOPULL;
 RI.Speed = GPIO_SPEED_FREQ_LOW;
 RI.Alternate = GPIO_MODE_INPUT;
 HAL_GPIO_Init(GPIOC, &RI);
 }
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Thanks !