MCF5253 Reference Manual, Rev. 1Freescale Semiconductor 26-1Chapter 26Real-Time ClockThis chapter provides the external signal descriptions, memory map, register descriptions, and functionaldescriptions of the Real-Time Clock module of the MCF5253.The real time clock (RTC) is a mixed-signal circuit which provides an indicator of time (in seconds) forvarious purposes in the system. The RTC does not stop running, even when the rest of the system ispowered down, so long as battery voltage (RTC_VDDA) remains above a certain threshold.26.1 Block DiagramFigure 26-1 is a block diagram of the functional organization of the RTC block.Figure 26-1. Real Time Clock Block Diagram26.2 External Signal DescriptionTable 26-1 describes the RTC external signals.26.3 Memory Map and Register DefinitionsThe RTC module’s register is accessible via the USB, ATA DMA, and clock integration module memoryspace. An RTC control and an RTC status bit are also included in the miscellaneous configuration register.Table 26-1. RTC SignalsSignal Name Abbreviation Function I/ORTC Crystal In RTC_CRIN 32.768 kHz crystal input clock. IRTC Crystal Out RTCCROUT 32.768 kHz crystal output. ORTC Supply Voltage RTC_VDDA Battery supply to RTC –RTC Ground RTCVSSA Ground for RTC supply –RTC LogicRTC_TIME1pps32.768 kHzRTC_CRINRTCCROUTRTC_VDDARTCVSSARTC Power Loss StatusRTC Power Loss ClearTo/From ATA-DMAConfig RegisterOscillatorin ATA-DMA
