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ST72F321 Datasheet(PDF) 57 Page - STMicroelectronics |
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ST72F321 Datasheet(HTML) 57 Page - STMicroelectronics |
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57 / 189 page  ST72321 57/189 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 register: CP[1:0] and SMS. 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 register. It can output three selectable frequencies on the BEEP pin (I/O port alternate function). Figure 36. 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 MCO BC1 BC0 MCCBCR BEEP SELECTION BEEP SIGNAL 1 0 TO WATCHDOG TIMER DIV 64 |
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