Backlight illumination adjust

The signal BL_control^[1] turns on the Backlight LED's controlled by the STLD40D^[2] IC on the display. To control the illuminace of the LED's its necessary to turn the LED's off and on using Pulse-Width-Modulation (PWM).

Keil MCBSTM32C board

On the Keil MCBSTM32C board the BL_control signal is connected to PB0 (Port B bit 0).

Looking in the Reference Maual on page 173 section 9.3.7 table 44 it's seen that Timer 3 Channel 3 has an alternate function on PB0.
To see Timer 3's possibilities on PB0 look on page 161 section 9.1.11 table 23 it's seen that timer 3 can use a GPIO pin as Output Compare Channel X when the pin is configured as Alternate Function Push-Pull.
To set PB0 as Alternate Function Push-Pull - See the GPIOx_CRL register on page 166.
To configure Timer 3 as continues PWM output timer see Page 371 section 15.3.9