MC68HC908QL4 Datasheet, PDF (107/226 Pages) Motorola, Inc – Microcontrollers

OSC During Break Interrupts
11.6 OSC During Break Interrupts
There are no status flags associated with the OSC module.
The system integration module (SIM) controls whether status bits in other modules can be cleared during
the break state. The BCFE bit in the break flag control register (BFCR) enables software to clear status
bits during the break state. See BFCR in the SIM section of this data sheet.
To allow software to clear status bits during a break interrupt, write a 1 to BCFE. If a status bit is cleared
during the break state, it remains cleared when the MCU exits the break state.
To protect status bits during the break state, write a 0 to BCFE. With BCFE cleared (its default state),
software can read and write registers during the break state without affecting status bits. Some status bits
have a two-step read/write clearing procedure. If software does the first step on such a bit before the
break, the bit cannot change during the break state as long as BCFE is cleared. After the break, doing the
second step clears the status bit.
11.7 I/O Signals
The OSC shares its pins with general-purpose input/output (I/O) port pins. See Figure 11-1 for port
location of these shared pins.
11.7.1 Oscillator Input Pin (OSC1)
The OSC1 pin is an input to the crystal oscillator amplifier, an input to the RC oscillator circuit, or an input
from an external clock source.
When the OSC is configured for internal oscillator, the OSC1 pin can be used as a general-purpose
input/output (I/O) port pin or other alternative pin function.
11.7.2 Oscillator Output Pin (OSC2)
For the XTAL oscillator option, the OSC2 pin is the output of the crystal oscillator amplifier.
When the OSC is configured for internal oscillator, external clock, or RC, the OSC2 pin can be used as a
general-purpose I/O port pin or other alternative pin function. When the oscillator is configured for internal
or RC, the OSC2 pin can be used to output BUSCLKX4.
Table 11-1. OSC2 Pin Function
Option
XTAL oscillator
External clock
Internal oscillator
or
RC oscillator
OSC2 Pin Function
Inverting OSC1
General-purpose I/O or alternative pin function
Controlled by OSC2EN bit
OSC2EN = 0: General-purpose I/O or alternative pin function
OSC2EN = 1: BUSCLKX4 output
MC68HC908QL4 Data Sheet, Rev. 7
Freescale Semiconductor
107