Clock configuration register 3
| USART1SW | USART1 clock source selection |
| I2C1SW | I2C1 clock source selection |
| I2C2SW | I2C2 clock source selection |
| CECSW | HDMI CEC clock source selection |
| TIM1SW | Timer1 clock source selection |
| TIM15SW | Timer15 clock source selection |
| TIM16SW | Timer16 clock source selection |
| TIM17SW | Timer17 clock source selection |