APB peripheral clock enable register 1
| TIM3EN | TIM3 timer clock enable |
| TIM4EN | TIM4 timer clock enable |
| TIM6EN | TIM6 timer clock enable |
| TIM7EN | TIM7 timer clock enable |
| USART5EN | USART5EN |
| USART6EN | USART6EN |
| RTCAPBEN | RTC APB clock enable |
| WWDGEN | WWDG clock enable |
| USBEN | USBEN |
| SPI2EN | SPI2 clock enable |
| SPI3EN | SPI3 clock enable |
| USART2EN | USART2 clock enable |
| USART3EN | USART3 clock enable |
| USART4EN | USART4 clock enable |
| I2C1EN | I2C1 clock enable |
| I2C2EN | I2C2 clock enable |
| I2C3EN | I2C3 clock enable |
| DBGEN | Debug support clock enable |
| PWREN | Power interface clock enable |