ST72321R6-Auto datasheet(82/243 Pages) STMICROELECTRONICS

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Main clock controller with real-time clock and beeper (MCC/RTC)

ST72321xx-Auto

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Doc ID 13829 Rev 1

Main clock controller with real-time clock and beeper

(MCC/RTC)

11.1

Introduction

The Main Clock Controller consists of three different 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 simultaneously.

11.2

Programmable CPU clock prescaler

The programmable CPU clock prescaler supplies the clock for the ST7 CPU and its internal

peripherals. It manages Slow power saving mode (see Section 8.2: Slow mode on page 62

for more details).

The prescaler selects the fCPU main clock frequency and is controlled by three bits in the

MCCSR register: CP[1:0] and SMS.

11.3

Clock-out capability

The clock-out capability is an alternate function of an I/O port pin that outputs a fCPU clock to

drive external devices. It is controlled by the MCO bit in the MCCSR register.

Caution:

When selected, the clock out pin suspends the clock during Active Halt mode.

11.4

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 depending directly on fOSC2 are available.

The whole functionality is controlled by four bits of the MCCSR 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: Active Halt and Halt modes on page 65 for

more details.

11.5

Beeper

The beep function is controlled by the MCCBCR register. It can output three selectable

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

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