ST7FOXU0 datasheet(27/123 Pages) STMICROELECTRONICS

27 / 123 page

ST7FOXU0

Supply, reset and clock management

27/123

Caution:

When the Read-Out Protection is enabled through an option bit (see Section 13.1: Option

bytes), these two bytes are protected against Read-out (including a re-write protection). In

Flash devices, when this protection is removed by reprogramming the option byte, these two

bytes are automatically erased.

Figure 8.

RC user calibration programming cycle

6.1.3

Auto Wake Up RC oscillator

The ST7FOX also contains an Auto Wake Up RC oscillator. This RC oscillator should be

enabled to enter Auto Wake-up from Halt mode.

The Auto Wake Up (AWU) RC oscillator can also be configured as the startup clock through

the CKSEL[1:0] option bits (see Section 13.1: Option bytes on page 110).

This is recommended for applications where very low power consumption is required.

Switching from one startup clock to another can be done in run mode as follows (see

Figure 9):

Case 1 Switching from internal RC to AWU

Set the RC/AWU bit in the CKCNTCSR register to enable the AWU RC oscillator

The RC_FLAG is cleared and the clock output is at 1.

Wait 3 AWU RC cycles till the AWU_FLAG is set

The switch to the AWU clock is made at the positive edge of the AWU clock signal

Once the switch is made, the internal RC is stopped

RCCLAT

ERASE CYCLE

WRITE CYCLE

RCCPGM

tPROG

READ OPERATION NOT POSSIBLE

WRITE OF

DATA LATCHES

READ OPERATION POSSIBLE

Internal

Programming

voltage

Byte 1 Byte 2

tPROG is typically 5 ms and max 10 ms

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