December 11, 1996
GENERAL RELEASE SPECIFICATION
MC68HC05J5
MODES OF OPERATION
MOTOROLA
REV 1.1
6-5
The contents of RAM and CPU registers are retained at supply voltages as low as
2.0 VDC. This is called the data-retention mode where the data is held, but the
device is not guaranteed to operate. The RESET pin must be held low during
data-retention mode.
6.6
COP WATCHDOG TIMER CONSIDERATIONS
The COP Watchdog Timer is active in all modes of operation if enabled by a mask
option. However, regardless of the mask option chosen, the COP Watchdog Timer
will be disabled if the voltage on the IRQ pin equals or exceeds the VTST voltage
level. Thus, emulation of applications that do not service the COP should only be
done with devices that have the COP Mask Option disabled. This prevents the
voltage level on the IRQ pin from enabling the COP which would cause a reset
and possibly change the operating mode of the device.
If the COP Watchdog Timer is selected by the mask option, any execution of the
STOP instruction (either intentional or inadvertent due to the CPU being dis-
turbed) will cause the oscillator to halt and prevent the COP Watchdog Timer from
timing out unless the STOP to HALT conversion feature is enabled. Therefore, it is
recommended that the STOP instruction should be converted to a HALT instruc-
tion if the COP Watchdog Timer is enabled.
If the COP Watchdog Timer is selected by the mask option, the COP will reset the
MCU when it times out. Therefore, it is recommended that the COP Watchdog
should be disabled for a system that must have intentional uses of the WAIT
Mode for periods longer than the COP time-out period.
The recommended interactions and considerations for the COP Watchdog Timer,
STOP instruction, and WAIT instruction are summarized in Table 6-2.
Table 6-2. COP Watchdog Timer Recommendations
less than VTST
WAIT Time less than
COP Time-Out
VTST = 1.8xVDD
Voltage on IRQ Pin
STOP Instruction
WAIT Time
THEN the
COP Watchdog Timer
should be as follows:
less than VTST
Disable COP
by mask option
converted to HALT
by mask option
Enable or disable COP
by mask option
WAIT Time more than
COP Time-Out
more than VTST
Acts as STOP or
converted to HALT
by mask option
COP is disabled
by IRQ input level
any length
WAIT Time
any length
WAIT Time
Acts as STOP
less than VTST
Disable COP
by mask option
converted to HALT
by mask option
IF the following conditions exist: