HC705V8GRSSLASHD datasheet(60/172 Pages) NXP

60 / 172 page

SECTION 6: RESETS

Page 49

MC68HC705V8 Specification Rev. 2.1

Table 6-1:

COP Watchdog Timer Recommendations

6.2.3.5

COP REGISTER

The COP register is shared with the MSB of an unimplemented User Interrupt Vector as

shown in Figure 6-3. Reading this location will return whatever user data has been

programmed at this location. Writing a “0” to the COPR bit in this location will clear the COP

watchdog timer.

Figure 6-3:

COP Watchdog Timer Location

6.2.4

LOW-VOLTAGE RESET (LVR)

The internal low voltage (LVR) reset is generated when VDD falls below the LVR threshold

VLVRI and will be released following a POR delay starting when VDD rises above VLVRR. The

LVR threshold is tested to be above the minimum operating voltage of the microcontroller

and is intended to assure that the CPU will be held in reset when the VBATT supply voltage

is below reasonable operating limits. However, it should be noted that the LVR monitors

VDD not VBATT. A mask option is provided to disable the LVR when the device is expected

to normally operate at low voltages. Note that the V

DD rise and fall slew rates (SVDDR and

VDDF) must be within the specification for proper LVR operation. If the specification is not

met, the circuit will operate properly following a delay of V

DD/Slew rate.

The LVR will generate the RST signal which will reset the CPU and other peripherals. As it

is not possible to determine the level of the internal VDD at the point VBATT recovers (and

POR is not intended to detect a loss of VDD), an LVR will always recover using a POR

delay. The low voltage reset will activate the internal pulldown device connected to the

RESET pin.

WAIT Time Less than

COP Time-Out

STOP Instruction

WAIT Time

THEN the

COP Watchdog Timer

should be as follows:

Disable COP

by mask option

converted to reset

Enable or disable COP

by mask option

WAIT Time More than

COP Time-Out

any length

WAIT Time

Acts as STOP

Disable COP

by mask option

converted to reset

IF the following conditions exist:

UNIMPLEMENTED VECTOR &

COP WATCHDOG TIMER

$3FF0

COPR

UNIMPLEMENTED

READ

WRITE

ADDR

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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