ST72344S4 datasheet(45/247 Pages) STMICROELECTRONICS

45 / 247 page

ST72344xx, ST2345xx

Supply, reset and clock management

Doc ID 12321 Rev 6

45/247

7.3.3

Internal RC oscillator

The device contains a high-precision internal RC oscillator. It must be calibrated to obtain

the frequency required in the application. This is done by software writing a calibration value

in the RCCRH and RCCRL Registers.

Whenever the microcontroller is reset, the RCCR returns to its default value (FF 03h), i.e.

each time the device is reset, the calibration value must be loaded in the RCCRH and

RCCRL registers. Predefined calibration values are stored in XFlash for 3 and 5V VDD

supply voltages at 25 °C, as shown in the following table:

Note:

To improve clock stability, it is recommended to place a decoupling capacitor between the

VDD and VSS pins.

These two 10-bit values are systematically programmed by ST.

RCCR0 and RCCR1 calibration values will be erased if the read-out protection bit is reset

after it has been set. See Section 4.5: Memory protection.

Caution:

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

to be recalibrated.

Refer to application note AN1324 for information on how to calibrate the RC frequency using

an external reference signal.

7.4

7.4.1

RC control register (RCCRH)

Reset value: 1111 1111 (FFh)

Bits 7:0 = CR[9:2] RC oscillator frequency adjustment bits

Table 9.

Calibration values

RCCR

Conditions

Address

RCCR0

VDD = 5 V

TA = 25 °C

fRC = 1 MHz

BEE0, BEE1

RCCR1

VDD = 3 V

TA = 25 °C

fRC = 1 MHz

BEE4, BEE5

CR9

CR8

CR7

CR6

CR5

CR4

CR3

CR2

Read/Write

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