MC908JL8CDWE Datasheet, PDF (80/212 Pages) Freescale Semiconductor, Inc – Microcontrollers

Oscillator (OSC)
OSCSEL — Oscillator Select Bit
OSCSEL selects the oscillator type for the MCU. The erased or unprogrammed state of this bit is
logic 1, selecting the crystal oscillator option. This bit is unaffected by reset.
1 = Crystal oscillator
0 = RC oscillator
Bits 6–0 — Should be left as logic 1’s.
NOTE
When Crystal oscillator is selected, the OSC2/RCCLK/PTA6/KBI6 pin is
used as OSC2; other functions such as PTA6/KBI6 will not be available.
6.2.1 XTAL Oscillator
The XTAL oscillator circuit is designed for use with an external crystal or ceramic resonator to provide
accurate clock source.
In its typical configuration, the XTAL oscillator is connected in a Pierce oscillator configuration, as shown
in Figure 6-2. This figure shows only the logical representation of the internal components and may not
represent actual circuitry. The oscillator configuration uses five components:
• Crystal, X₁
• Fixed capacitor, C₁
• Tuning capacitor, C₂ (can also be a fixed capacitor)
• Feedback resistor, R_B
• Series resistor, R_S (optional)
From SIM
To SIM
To SIM
2OSCOUT
OSCOUT
SIMOSCEN
XTALCLK
÷2
MCU
OSC1
OSC2
R_B
X₁
C₁
R_S*
*R_S can be zero (shorted) when used with higher-frequency crystals.
Refer to manufacturer’s data.
See Chapter 17 for component value requirements.
C₂
Figure 6-2. XTAL Oscillator External Connections
The series resistor (R_S) is included in the diagram to follow strict Pierce oscillator guidelines and may not
be required for all ranges of operation, especially with high frequency crystals. Refer to the crystal
manufacturer’s data for more information.
MC68HC908JL8/JK8 • MC68HC08JL8/JK8 • MC68HC908KL8 Data Sheet, Rev. 3.1
80
Freescale Semiconductor