Clock control register
| HSION | HSI16 clock enable |
| HSIKERON | HSI16 always enable for peripheral kernels |
| HSIRDY | HSI16 clock ready flag |
| HSIDIV | HSI16 clock division factor |
| HSEON | HSE clock enable |
| HSERDY | HSE clock ready flag |
| HSEBYP | HSE crystal oscillator bypass |
| CSSON | Clock security system enable |
| PLLON | PLL enable |
| PLLRDY | PLL clock ready flag |