Atmel ARM-Based Evaluation Kit for SAM4S16C, 32-Bit ARM® Cortex® Microcontroller ATSAM4S-WPIR-RD ATSAM4S-WPIR-RD 数据表

SAM4S Series [DATASHEET]

Atmel-11100G-ATARM-SAM4S-Datasheet_27-May-14

530

CKGR_MCFR

0x400E0424

Read/Write 

This register can only be written if the WPEN bit is cleared in 

Gives the number of Main Clock cycles within 16 Slow Clock periods.

0: MAINF value is not valid or the Main Oscillator is disabled or a measure has just been started by means of RCMEAS.
1: The Main Oscillator has been enabled previously and MAINF value is available.

Note: To ensure that a correct value is read on the MAINF field, the MAINFRDY flag must be read at 1 then another read access must 

be performed on the register to get a stable value on the MAINF field.

0: No effect.
1: Restarts measuring of the main RC frequency. MAINF will carry the new frequency as soon as a low to high transition 

occurs on the MAINFRDY flag.
The measure is performed on the main frequency (i.e. not limited to RC oscillator only), but if the main clock frequency 

source is the fast crystal oscillator, the restart of measuring is not needed because of the well known stability of crystal 

oscillators.

31

30

29

28

27

26

25

24

–

–

–

–

–

–

–

–

23

22

21

20

19

18

17

16

–

–

–

RCMEAS

–

–

–

MAINFRDY

15

14

13

12

11

10

9

8

MAINF

7

6

5

4

3

2

1

0

MAINF