MC68HLC908QY4 Datasheet, PDF (95/182 Pages) Motorola, Inc – Microcontrollers

Oscillator During Break Mode
11.6 Oscillator During Break Mode
The oscillator continues to drive BUSCLKX2 and BUSCLKX4 when the device enters the break state.
11.7 CONFIG2 Options
Two CONFIG2 register options affect the operation of the oscillator module: OSCOPT1 and OSCOPT0.
All CONFIG2 register bits will have a default configuration. Refer to Chapter 5 Configuration Register
(CONFIG) for more information on how the CONFIG2 register is used.
Table 11-2 shows how the OSCOPT bits are used to select the oscillator clock source.
Table 11-2. Oscillator Modes
OSCOPT1
0
0
1
1
OSCOPT0
0
1
0
1
Oscillator Modes
Internal Oscillator
External Oscillator
External RC
External Crystal
11.8 Input/Output (I/O) Registers
The oscillator module contains these two registers:
1. Oscillator status register (OSCSTAT)
2. Oscillator trim register (OSCTRIM)
11.8.1 Oscillator Status Register
The oscillator status register (OSCSTAT) contains the bits for switching from internal to external clock
sources.
Address: $0036
Bit 7
6
5
Read:
R
R
R
Write:
Reset: 0
0
0
R
= Reserved
4
3
2
R
R
R
0
0
0
= Unimplemented
1
ECGON
Bit 0
ECGST
0
0
Figure 11-4. Oscillator Status Register (OSCSTAT)
ECGON — External Clock Generator On Bit
This read/write bit enables external clock generator, so that the switching process can be initiated. This
bit is forced low during reset. This bit is ignored in monitor mode with the internal oscillator bypassed.
1 = External clock generator enabled
0 = External clock generator disabled
ECGST — External Clock Status Bit
This read-only bit indicates whether or not an external clock source is engaged to drive the system
clock.
1 = An external clock source engaged
0 = An external clock source disengaged
MC68HLC908QY/QT Family Data Sheet, Rev. 3
Freescale Semiconductor
95