MC9S08SG8 Datasheet, PDF (191/310 Pages) Freescale Semiconductor, Inc – Microcontrollers

Real-Time Counter (S08RTCV1)
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.
Wait Mode
The RTC continues to run in wait mode if enabled before executing the WAIT instruction. Therefore, the
RTC can be used to 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.
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 be used to 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 both 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.
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.
MC9S08SG8 MCU Series Data Sheet, Rev. 0
Freescale Semiconductor
191