Freescale Semiconductor MCF51QE128RM Chapter Real-Time Counter S08RTCV1, ADC Hardware Trigger

Models: MCF51QE128RM

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Chapter 14

Real-Time Counter (S08RTCV1)

14.1Introduction

The real-time counter (RTC) consists of one 8-bit counter, one 8-bit comparator, several binary-based and decimal-based prescaler dividers, three clock sources, and one programmable periodic interrupt. This module can be used for time-of-day, calendar, or any task scheduling functions. It can also serve as a cyclic wake up from low-power modes without the need of external components.

14.1.1ADC Hardware Trigger

The RTC can be enabled as a hardware trigger for the ADC module by setting ADCSC2[ADTRG]. When enabled, the ADC is triggered each time RTCINT matches RTCMOD. The RTC interrupt does not have to be enabled to trigger the ADC.

14.1.2RTC Clock Sources

The RTC module on MCF51QE128 Series can be clocked from ICSIRCLK, OSCOUT, or the LPO. In this chapter, ERCLK is replaced by OSCOUT for this MCU.

14.1.3RTC Modes of Operation

All clock sources are available in all modes except stop2. The OSCOUT and LPO can be enabled as the clock source of the RTC in stop2.

14.1.3.1RTC Status after Stop2 Wakeup

The registers associated with the RTC are unaffected after a stop2 wakeup.

14.1.3.2Clocks in Stop Modes

In the MCF51QE128 Series, LPO and OSCOUT can be used in stop2 and stop3. IRCLK is available only in stop3.

14.1.4RTC Clock Gating

The bus clock to the RTC can be gated on and off with SCGC2[RTC]. This bit is set after any reset, which enables the bus clock to this module. To conserve power, the RTC bit can be cleared to disable the clock to this module when not in use. See Section 5.6, “Peripheral Clock Gating,” for details.

MCF51QE128 MCU Series Reference Manual, Rev. 3

Freescale Semiconductor

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Freescale Semiconductor MCF51QE128RM manual Chapter Real-Time Counter S08RTCV1, ADC Hardware Trigger, RTC Clock Sources