HC705C9AGRSSLASHD datasheet(59/157 Pages) NXP

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General Release Specification

COP During Stop Mode

MC68HC705C9A — Rev. 2.0

Resets

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.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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