ST72321 datasheet(57/185 Pages) STMICROELECTRONICS

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ST72321

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10.2 MAIN CLOCK CONTROLLER WITH REAL TIME CLOCK AND BEEPER (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.

10.2.1 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 8.2 SLOW MODE for more details).

The prescaler selects the fCPU main clock frequen-

cy and is controlled by three bits in the MCCSR

10.2.2 Clock-out Capability

The clock-out capability is an alternate function of

an I/O port pin that outputs a fOSC2 clock to drive

external devices. It is controlled by the MCO bit in

the MCCSR register.

CAUTION: When selected, the clock out pin sus-

pends the clock during ACTIVE-HALT mode.

10.2.3 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 fOSC2 are available. The whole

functionality is controlled by four bits of the MCC-

SR register: TB[1:0], OIE and OIF.

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

the ST7 enters ACTIVE-HALT mode when the

HALT instruction is executed. See Section 8.4 AC-

TIVE-HALT AND HALT MODES for more details.

10.2.4 Beeper

The beep function is controlled by the MCCBCR

on the BEEP pin (I/O port alternate function).

Figure 35. Main Clock Controller (MCC/RTC) Block Diagram

DIV 2, 4, 8, 16

MCC/RTC INTERRUPT

SMS

CP1 CP0

TB1

TB0

OIE

OIF

CPU CLOCK

MCCSR

12-BIT MCC RTC

COUNTER

TO CPU AND

PERIPHERALS

fOSC2

fCPU

MCO

BC1 BC0

MCCBCR

BEEP

SELECTION

BEEP SIGNAL

WATCHDOG

TIMER

DIV 64

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