mc68hc05pl4b Freescale Semiconductor, Inc, mc68hc05pl4b Datasheet - Page 50

• Manufacturer Part Number: mc68hc05pl4b
• Description: Low-cost Single-chip Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

GENERAL RELEASE SPECIFICATION
8-2
FMODE — Fast Mode RC select
OSCF — OSC running Flag
RCF — RC Running Flag
CKOSC — ChecK OSC
FMODE selects the oscillating frequency of the internal RC. After power-on-
reset, the default setting is 500kHz.
This bit is set when the external clock (External/crystal) from OSC1 is on.
See also CKOSC bit below.
This bit is set when the internal RC clock is on.
The CKOSC bit enables the internal logic for external clock selection. The pro-
cedure below should be followed when switching from RC to external clock.
1. Set the CKSEL1 and CKSEL2 bits for external clock source.
2. If crystal option is used — set the 8-bit timer for counting crystal
3. Write a “1” to the CKOSC bit and check for OSCF bit set.
4. If the OSCF bit is not set, no external clock is available, the internal RC
1 = Internal RC oscillates at 500kHz
0 = Internal RC oscillates at 20kHz
stabilization delay (typically 4064 clock cycles).
clock will be used as the system clock, irrespective of the setting for
CKSEL1 and CKSEL2.
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
SYSTEM CLOCKS
April 30, 1998
MC68HC05PL4
REV 2.0