mc68hc908qb4 Freescale Semiconductor, Inc, mc68hc908qb4 Datasheet - Page 100

• Manufacturer Part Number: mc68hc908qb4
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Oscillator Module (OSC)
11.8 Registers
The oscillator module contains two registers:
11.8.1 Oscillator Status and Control Register
The oscillator status and control register (OSCSC) contains the bits for switching between internal and
external clock sources. If the application uses an external crystal, bits in this register are used to select
the crystal oscillator amplifier necessary for the desired crystal. While running off the internal clock source,
the user can use bits in this register to select the internal clock source frequency.
OSCOPT1:OSCOPT0 — OSC Option Bits
ICFS1:ICFS0 — Internal Clock Frequency Select Bits
100
•
•
These read/write bits allow the user to change the clock source for the MCU. The default reset
condition has the bus clock being derived from the internal oscillator. See
Clock Switching
These read/write bits enable the frequency to be increased for applications requiring a faster bus clock
when running off the internal oscillator. The WAIT instruction has no effect on the oscillator logic.
BUSCLKX2 and BUSCLKX4 continue to drive to the SIM module.
Oscillator status and control register (OSCSC)
Oscillator trim register (OSCTRIM)
Reset:
Read:
Write:
OSCOPT1
ICFS1
for information on changing clock sources.
Figure 11-4. Oscillator Status and Control Register (OSCSC)
OSCOPT1
0
0
1
1
0
0
1
1
Bit 7
0
= Unimplemented
OSCOPT0
OSCOPT0
ICFS0
6
0
0
1
0
1
0
1
0
1
MC68HC908QB8 Data Sheet, Rev. 2
ICFS1
4.0 MHz — default reset condition
8.0 MHz
12.8 MHz
Reserved
Internal oscillator (frequency selected using ICFSx bits)
External oscillator clock
External RC
External crystal (range selected using ECFSx bits)
5
0
ICFS0
4
0
Internal Clock Frequency
Oscillator Modes
ECFS1
3
0
ECFS0
2
0
ECGON
11.3.2.2 Internal to External
1
0
Freescale Semiconductor
ECGST
Bit 0
0