MC908JL8CDWE Datasheet, PDF (82/212 Pages) Freescale Semiconductor, Inc – Microcontrollers

Oscillator (OSC)
NOTE
The internal oscillator is a free running oscillator and is available after each
POR or reset. It is turned-off in stop mode by setting the STOP_ICLKDIS
bit in CONFIG2 (see 3.4 Configuration Register 2 (CONFIG2)).
6.4 I/O Signals
The following paragraphs describe the oscillator I/O signals.
6.4.1 Crystal Amplifier Input Pin (OSC1)
OSC1 pin is an input to the crystal oscillator amplifier or the input to the RC oscillator circuit.
6.4.2 Crystal Amplifier Output Pin (OSC2/RCCLK/PTA6/KBI6)
For the XTAL oscillator, OSC2 pin is the output of the crystal oscillator inverting amplifier.
For the RC oscillator, OSC2 pin can be configured as a general purpose I/O pin PTA6, or the output of
the RC oscillator, RCCLK.
Oscillator
XTAL
RC
OSC2 pin function
Inverting OSC1
Controlled by PTA6EN bit in PTAPUE ($000D)
PTA6EN = 0: RCCLK output
PTA6EN = 1: PTA6/KBI6
6.4.3 Oscillator Enable Signal (SIMOSCEN)
The SIMOSCEN signal comes from the system integration module (SIM) and enables/disables the XTAL
oscillator circuit or the RC-oscillator.
6.4.4 XTAL Oscillator Clock (XTALCLK)
XTALCLK is the XTAL oscillator output signal. It runs at the full speed of the crystal (f_XCLK) and comes
directly from the crystal oscillator circuit. Figure 6-2 shows only the logical relation of XTALCLK to OSC1
and OSC2 and may not represent the actual circuitry. The duty cycle of XTALCLK is unknown and may
depend on the crystal and other external factors. Also, the frequency and amplitude of XTALCLK can be
unstable at start-up.
6.4.5 RC Oscillator Clock (RCCLK)
RCCLK is the RC oscillator output signal. Its frequency is directly proportional to the time constant of the
external R and C. Figure 6-3 shows only the logical relation of RCCLK to OSC1 and may not represent
the actual circuitry.
6.4.6 Oscillator Out 2 (2OSCOUT)
2OSCOUT is same as the input clock (XTALCLK or RCCLK). This signal is driven to the SIM module.
MC68HC908JL8/JK8 • MC68HC08JL8/JK8 • MC68HC908KL8 Data Sheet, Rev. 3.1
82
Freescale Semiconductor