ST7FLU05MCE View Datasheet(PDF) - STMicroelectronics

Part Name

Description

MFG CO.

ST7FLU05MCE

8-bit low cost, low pin-count MCU for automotive, with single voltage Flash memory, ADC, timers

STMicroelectronics 

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Supply, reset and clock management

ST7LUS5, ST7LU05, ST7LU09

Caution: If the voltage or temperature conditions change in the application, the frequency may need

to be recalibrated.

Refer to application note AN2326 for information on how to calibrate the RC frequency using

an external reference signal.

The ST7LUxx 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 RC oscillator can also be configured as the startup clock through the

CKSEL[1:0] option bits (see Section 14.1 on page 131).

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 12):

t(s) Case 1: Switching from internal RC to AWU

c 1. Set the RC/AWU bit in the CKCNTCSR register to enable the AWU RC oscillator.

du 2. The RC_FLAG is cleared and the clock output is at 1.

ro ) 3. Wait 3 AWU RC cycles until the AWU_FLAG is set.

P t(s 4. The switch to the AWU clock is made at the positive edge of the AWU clock signal.

te c 5. Once the switch is made, the internal RC is stopped.

sole rodu Case 2: Switching from AWU RC to internal RC

b P 1. Reset the RC/AWU bit to enable the internal RC oscillator.

- O te 2. Using a 4-bit counter, wait until 8 internal RC cycles have elapsed. The counter is

) le running on internal RC clock.

t(s o 3. Wait until the AWU_FLAG is cleared (1 AWU RC cycle) and the RC_FLAG is set (2 RC

s cycles).

c b 4. The switch to the internal RC clock is made at the positive edge of the internal RC clock

du O signal.

ro ) - 5. Once the switch is made, the AWU RC is stopped.

P t(s Note: 1 When the internal RC is not selected, it is stopped so as to save power consumption.

te c 2 When the internal RC is selected, the AWU RC is turned on by hardware when entering

le du Auto Wake-up from Halt mode.

so ro 3 When the external clock is selected, the AWU RC oscillator is always on.

Ob te P Figure 9. Clock switching

le Set RC/AWU

Obso Internal RC Poll AWU_FLAG until set

AWU RC

AWU RC

Reset RC/AWU

Poll RC_FLAG until set

Internal RC

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