APB2 peripheral clock enable register
| SYSCFGEN | System configuration controller clock enable bit |
| TIM21EN | TIM21 timer clock enable bit |
| TIM22EN | TIM22 timer clock enable bit |
| FWEN | Firewall clock enable bit |
| ADCEN | ADC clock enable bit |
| SPI1EN | SPI1 clock enable bit |
| USART1EN | USART1 clock enable bit |
| DBGEN | DBG clock enable bit |