Oscillator Module (OSC)
MC68HC908QL4 MC68HC908QL3 MC68HC908QL2 Data Sheet, Rev. 4
106
Freescale Semiconductor
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
.
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.
MCU
R
EXT
OSC1
EXTERNAL RC
OSCILLATOR
EN
RCCLK
÷ 2
BUSCLKX2
BUSCLKX4
V
DD
1
0
OSC2EN
OSC2- available for alternative pin function
See the electricals section
for component value.
0
1
INTCLK
OSCOPT = EXTERNAL RC SELECTED
SIMOSCEN (internal signal) OR
OSCENINSTOP (bit located in
configuration register))
ALTERNATIVE
PIN FUNCTION