NXP Semiconductors MC9S08QL4, Reference Manual

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MC9S08QL8 MCU Series Reference Manual, Rev. 1
NXP Semiconductors 173
Chapter 13
Real-Time Counter (S08RTCV1)
13.1 Introduction
The real-time counter (RTC) consists of one 8-bit counter, one 8-bit comparator, several binary-based and
decimal-based prescaler dividers, two 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
wakeup from low power modes without the need of external components.
13.1.1 ADC Hardware Trigger
This RTC can be enabled as a hardware trigger for the ADC module by setting the ADTRG bit in the
ADCSC2 register. When enabled, the ADC will be triggered every time RTCINT matches RTCMOD. The
RTC interrupt does not have to be enabled to trigger the ADC.
13.1.2 RTC Clock Sources
The RTC module on MC9S08QL8 series can be clocked from the ICSIRCLK, OSCOUT or the LPO.
ICSIRCLK is connected to the IRCLK input and OSCOUT is connected to ERCLK input.
ICSERCLK is not available as a source to the RTC in this MCU.
13.1.3 RTC 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.
13.1.4 RTC Status after Stop2 Wakeup
The registers associated with the RTC will be unaffected after a stop2 wakeup.
13.1.5 RTC Clock Gating
The bus clock to the RTC can be gated on and off using the RTC bit in SCGC2. 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. If the bus clock is not used as the RTC clock source, the bus clock
must still be enabled to the RTC for proper operation. Interrupts from the RTC will not occur if the bus
clock is gated off. See
Section 5.7, Peripheral Clock Gating for details.