MC68HC705C9A_1 Datasheet, PDF (59/157 Pages) Freescale Semiconductor, Inc – General Release Specification

Freescale Semiconductor, Inc.
General Release Specification
COP During Stop Mode
5.10 COP During Stop Mode
Stop mode disables the oscillator circuit and thereby turns the clock off
for the entire device. The COP counter will be reset when stop mode is
entered. If a reset is used to exit stop mode, the COP counter will be
reset after the 4064 cycles of delay after stop mode. If an IRQ is used to
exit stop mode, the COP counter will not be reset after the 4064-cycle
delay and will have that many cycles already counted when control is
returned to the program.
In the event that an inadvertent STOP instruction is executed, neither
COP will allow the system to recover. The MC68HC705C9A offers two
solutions to this problem, one available in C9A mode (see 5.10.1 Clock
Monitor Reset) and one available in C12A mode (see 5.10.2 STOP
Instruction Disable Option).
5.10.1 Clock Monitor Reset
When configured as a C9A, the clock monitor circuit can provide a
system reset if the clock stops for any reason, including stop mode.
When the CME bit in the C9A COP control register is set, the clock
monitor detects the absence of the internal bus clock for a certain period
of time. The timeout period is dependent on the processing parameters
and varies from 5 µs to 100 µs, which implies that systems using a bus
clock rate of 200 kHz or less should not use the clock monitor.
If a slow or absent clock is detected, the clock monitor causes a system
reset. The reset is issued to the external system via the bidirectional
RESET pin for four bus cycles if the clock is slow or until the clocks
recover in the case where the clocks are absent.
5.10.2 STOP Instruction Disable Option
On the ROM device MC68HC05C12A, stop mode can be disabled by
mask option. This causes the CPU to interpret the STOP instruction as
a NOP so the device will never enter stop mode; if the user code is not
being executed properly, the COP will provide a system reset.
MC68HC705C9A — Rev. 2.0
Resets
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