ST62T53B datasheet(19/75 Pages) STMICROELECTRONICS

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ST62T53B/T60B/T63B ST62E60B

CLOCK SYSTEM (Cont’d)

Oscillator Control Registers

Address: DCh

—

Write only

Bit 7-4. These bits are not used.

Bit 3. Reserved. Cleared at Reset. THIS BIT

MUST BE SET TO 1 BY USER PROGRAM to

achieve lowest power consumption.

Bit 2. Reserved. Must be kept low.

RS1-RS0. These bits select the division ratio of

the Oscillator Divider in order to generate the inter-

nal frequency. The following selctions are availa-

ble:

Note: Care is required when handling the OSCR

son, it is not allowed to change the OSCR contents

while executing interrupt service routine, as the

service routine cannot save and then restore its

previous content. If it is impossible to avoid the

writing of this register in interrupt service routine,

an image of this register must be saved in a RAM

location, and each time the program writes to

OSCR it must write also to the image register. The

image register must be written first, so if an inter-

rupt occurs between the two instructions the

OSCR is not affected.

Figure 10. Clock Circuit Block Diagram

---

OSCR

RS1

RS0

RS1

RS0

Division Ratio

MAIN

OSCILLATOR

Core

:13

:12

Timer

Watchdog

POR

fINT

ADC

AR Timer

SPI

OSCILLATOR

DIVIDE R

RS0, RS1

OSCin

OSCout

fOSC

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