CSB1000JA datasheet(52/153 Pages) STMICROELECTRONICS

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ST72334J/N, ST72314J/N, ST72124J

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14.2 MAIN CLOCK CONTROLLER WITH REAL TIME CLOCK TIMER (MCC/RTC)

The Main Clock Controller consists of three differ-

ent functions:

a programmable CPU clock prescaler

a clock-out signal to supply external devices

a real time clock timer with interrupt capability

Each function can be used independently and si-

multaneously.

14.2.1 Programmable CPU clock prescaler

The programmable CPU clock prescaler supplies

the clock for the ST7 CPU and its internal periph-

erals. It manages SLOW power saving mode (See

Section 11.2 "SLOW MODE" on page 35 for more

details).

The prescaler selects the fCPU main clock frequen-

cy and is controlled by three bits in the MISCR1

CAUTION: The prescaler does not act on the CAN

peripheral clock source. This peripheral is always

supplied by the fOSC/2 clock source.

14.2.2 Clock-out capability

The clock-out capability is an alternate function of

an I/O port pin that outputs a fOSC/2 clock to drive

external devices. It is controlled by the MCO bit in

the MISCR1 register.

CAUTION: When selected, the clock out pin sus-

pends the clock during ACTIVE-HALT mode.

14.2.3 Real time clock timer (RTC)

The counter of the real time clock timer allows an

interrupt to be generated based on an accurate

real time clock. Four different time bases depend-

ing directly on fOSC are available. The whole func-

tionality is controlled by four bits of the MCCSR

When the RTC interrupt is enabled (OIE bit set),

the ST7 enters ACTIVE-HALT mode when the

HALT instruction is executed. See Section 11.4

"ACTIVE-HALT AND HALT MODES" on page 37

for more details.

Figure 30. Main Clock Controller (MCC/RTC) Block Diagram

DIV 2, 4, 8, 16

MCC/RTC INTERRUPT

DIV 2

SMS

CP1 CP0

TB1 TB0

OIE

OIF

CPU CLOCK

MISCR1

RTC

COUNTER

TO CPU AND

PERIPHERALS

fOSC

fCPU

MCO

PORT

FUNCTION

ALTERNATE

MCO

MCCSR

fOSC/2

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