First, he stressed: Peripheral clock enable must be initialized before! ! ! ! ! ! !
In a reference to this explanation,
To set its registers after "ARM chip, usually to the peripheral clock (i.e., to use the peripherals).
STM32, LPC1XXX etc. are like, The goal is to conserve power, the use of so-called clock gating technique.
The register is based on what?
Of course the flip-flop! ! ! To be exact D flip-flop
The assignment is necessarily trigger the clock, and the clock register is provided by the bus clock, the bus clock that is not the case, you give it the value of the register is not read. In other words, only brought the clock, trigger values can be rewritten so that the register will work.
Why would someone say that before I learned why the 51 time clock can not make it?
When did we learn 51, which will focus on power consumption, we run up a program on the list, but for most manufacturers, the vast majority are not concerned about power consumption. However the STM32 different, in order to reduce power consumption, ST companies to save power, the use of so-called clock gating technique, which also involves the synchronization circuit. A synchronizing circuit there is always clocked.
By default these are disable the clock. If you want to use it, you first need to enable.
We can also put this clock simpler than a door, STM32 is the reason why low-power, it is because he put all the doors are default settings to disable, at which time you need to use the door, which door you can open, that What used peripherals, simply open the corresponding peripheral clock on it, the other to be useless or disable, so that energy consumption will be reduced.