
NON-DISCLOSURE
AGREEMENT
REQUIRED
Oscillators/Clock Distributions
General Release Specification
MC68HC(7)05L5 — Rev. 2.0
92
Oscillators/Clock Distributions
MOTOROLA
7.5.2.2 XOSC with FOSCE = 0
If XOSC is the system clock, clearing FOSCE will stop OSC and preset
the 7-bit divider and 6-bit POR counter to $0078. Execution will continue
with XOSC and when FOSCE is set again, OSC will re-start. When the
POR counter overflows, FTUP is set, signaling that OSC is stable and
OSC can be used as the system clock. The stabilization time will be 8072
counts.
7.5.2.3 XOSC with FOSCE = 0 and STOP
If XOSC is the system clock and FOSCE is cleared, further power
reduction can be achieved by executing the STOP instruction. In this
case, OSC is stopped, the 7-bit divider and 6-bit POR counter are preset
to $0078 (since FOSCE = 0) and execution is halted. Exiting STOP with
external IRQ does not re-start the OSC; however, execution begins
immediately using XOSC. OSC may be re-started by setting FOSCE.
When the POR counter overflows, FTUP will be set, signaling that OSC
is stable and can be used as the system clock. The stabilization time will
be 8072 counts.
7.5.2.4 Stop Mode and Wait Mode
During stop mode, the main oscillator (OSC) is shut down and the clock
path from the second oscillator (XOSC) is disconnected. All modules
except timebase are halted. Entering stop mode clears the FTUP flag in
the MISC register and initializes the POR counter. Stop mode is exited
by RESET, IRQ1, IRQ2, KWI, SSPI (slave mode), or timebase interrupt.
If OSC is selected as the system clock source during stop mode, CPU
resumes after the overflow of the POR counter and this overflow also
sets the FTUP status flag.
If XOSC is selected as the system clock source during stop mode, no
stop recovery time is required for exiting stop mode because XOSC
never stops. Re-start of the main oscillator depends on the FOSCE bit.
During wait mode, only the CPU clocks are halted and the peripheral
modules are not affected. Wait mode is exited by RESET and any
interrupts.
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Freescale Semiconductor, Inc.
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