APB1 peripheral clock enable register
| TIM2EN | Timer2 clock enable bit |
| TIM3EN | Timer 3 clock enbale bit |
| TIM6EN | Timer 6 clock enable bit |
| TIM7EN | Timer 7 clock enable bit |
| WWDGEN | Window watchdog clock enable bit |
| SPI2EN | SPI2 clock enable bit |
| USART2EN | UART2 clock enable bit |
| LPUART1EN | LPUART1 clock enable bit |
| USART4EN | USART4 clock enable bit |
| USART5EN | USART5 clock enable bit |
| I2C1EN | I2C1 clock enable bit |
| I2C2EN | I2C2 clock enable bit |
| PWREN | Power interface clock enable bit |
| I2C3EN | I2C3 clock enable bit |
| LPTIM1EN | Low power timer clock enable bit |