14.1.6Features

Features of the RTC module include:

8-bit up-counter

8-bit modulo match limit

Software controllable periodic interrupt on match

Three software selectable clock sources for input to prescaler with selectable binary-based and decimal-based divider values

1-kHz internal low-power oscillator (LPO)

External clock (ERCLK)

32-kHz internal clock (IRCLK)

14.1.7Modes of Operation

This section defines the operation in stop, wait and background debug modes.

14.1.7.1Wait Mode

The RTC continues to run in wait mode if enabled before executing the appropriate instruction. Therefore, the RTC can bring the MCU out of wait mode if the real-time interrupt is enabled. For lowest possible current consumption, the RTC should be stopped by software if not needed as an interrupt source during wait mode.

14.1.7.2Stop Modes

The RTC continues to run in stop2 or stop3 mode if the RTC is enabled before executing the STOP instruction. Therefore, the RTC can bring the MCU out of stop modes with no external components, if the real-time interrupt is enabled.

The LPO clock can be used in stop2 and stop3 modes. ERCLK and IRCLK clocks are only available in stop3 mode.

Power consumption is lower when all clock sources are disabled, but in that case, the real-time interrupt cannot wake up the MCU from stop modes.

14.1.7.3Active Background Mode

The RTC suspends all counting during active background mode until the microcontroller returns to normal user operating mode. Counting resumes from the suspended value as long as the RTCMOD register is not written and the RTCPS and RTCLKS bits are not altered.

MCF51QE128 MCU Series Reference Manual, Rev. 3

284

Freescale Semiconductor

Get the latest version from freescale.com

Page 284
Image 284
Freescale Semiconductor MCF51QE128RM manual Features, Active Background Mode