HCS08 datasheet(191/316 Pages) NXP

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Real-Time Counter (S08RTCV1)

MC9S08SG8 MCU Series Data Sheet, Rev. 8

Freescale Semiconductor

191

13.1.1

Features

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)

13.1.2

Modes of Operation

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

13.1.2.1

Wait 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.

13.1.2.2

Stop 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.

13.1.2.3

Active 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.

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