AHB1 peripheral clock register
| GPIOAEN | IO port A clock enable |
| GPIOBEN | IO port B clock enable |
| GPIOCEN | IO port C clock enable |
| GPIODEN | IO port D clock enable |
| GPIOEEN | IO port E clock enable |
| GPIOHEN | IO port H clock enable |
| CRCEN | CRC clock enable |
| DMA1EN | DMA1 clock enable |
| DMA2EN | DMA2 clock enable |