MC908QY8CDWE Datasheet, PDF (100/232 Pages) Freescale Semiconductor, Inc – Addendum to MC68HC908QB8, rev. 3

Oscillator Module (OSC)
11.3.5 RC Oscillator
The RC oscillator circuit is designed for use with an external resistor (R_EXT) to provide a clock source with
a tolerance within 25% of the expected frequency. See Figure 11-3.
The capacitor (C) for the RC oscillator is internal to the MCU. The R_EXT value must have a tolerance of
1% or less to minimize its effect on the frequency.
In this configuration, the OSC2 pin can be used as general-purpose input/output (I/O) port pins or other
alternative pin function. The OSC2EN bit can be set to enable the OSC2 output function on the pin.
Enabling the OSC2 output can affect the external RC oscillator frequency, f_RCCLK.
SIMOSCEN (INTERNAL SIGNAL) OR
OSCENINSTOP (BIT LOCATED IN
CONFIGURATION REGISTER)
INTCLK
0
OSCOPT = EXTERNAL RC SELECTED
BUSCLKX4
BUSCLKX2
1
EN
EXTERNAL RC
OSCILLATOR
RCCLK
÷2
1
0
ALTERNATIVE
PIN FUNTION
MCU
OSC2EN
OSC1
OSC2 — AVAILABLE FOR ALTERNATIVE PIN FUNCTION
V_DD
R_EXT
See the electricals section for component value.
Figure 11-3. RC Oscillator External Connections
11.4 Interrupts
There are no interrupts associated with the OSC module.
11.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
11.5.1 Wait Mode
The OSC module remains active in wait mode.
11.5.2 Stop Mode
The OSC module can be configured to remain active in stop mode by setting OSCENINSTOP located in
a configuration register.
MC68HC908QB8 Data Sheet, Rev. 3
98
Freescale Semiconductor