mc68hc05pl4b Freescale Semiconductor, Inc, mc68hc05pl4b Datasheet - Page 36

• Manufacturer Part Number: mc68hc05pl4b
• Description: Low-cost Single-chip Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

GENERAL RELEASE SPECIFICATION
5.3.3 Illegal Address Reset
5-4
Use the following formula to calculate the COP time-out period:
The clock input to the watchdog system is derived from the output of the Timer8,
therefore a reset or preset of Timer8 may affect the COP watchdog time-out
period.
The COP Watchdog reset will assert the pulldown device to pull the RESET pin
low for 3-4 cycles of the internal bus clock.
The COP reset can be enable or disable by the COPON bit in MISCR. The MISCR
is in Figure 5-5.
COPON — COP On
The COP Watchdog system is not designed to operate in STOP mode, therefore it
should be disabled before entering STOP mode by clearing the COPON bit.
Entering STOP mode with COP watchdog enabled will cause an internal reset of
the MCU.
An opcode fetch from an address that is not in the ROM (locations $0E00–$1DFF
and $1FF0-$1FFF) or the RAM (locations $0020–$011F) generates an illegal
address reset. The illegal address reset will assert the pulldown device to pull the
RESET pin low for 3-4 cycles of the internal bus clock.
RESET
MICSR
$001C
Since the COP Watchdog system is derived from the 8-bit Timer system, the
T8EN bit in the Timer8 Control and Status register (bit3 of $0D) must be set for
COPON bit to have any affect.
COPON can be set to enable the COP watchdog system. Once set, the watch-
dog system cannot be disabled other than by a power-on reset or external
reset. After a reset the COPON bit is cleared and the COP watchdog system is
disabled.
1 = COP Watchdog enabled.
0 = COP Watchdog disabled.
Figure 5-5. Miscellaneous Control and Status Register (MICSR)
W
R
IRQEN
BIT 7
0
COP Time-out Period = (prescaler x 256 x 8)
Freescale Semiconductor, Inc.
For More Information On This Product,
IRQS
BIT 6
where prescaler is the Timer8 prescaler value
0
Go to: www.freescale.com
TCMPEN
BIT 5
April 30, 1998
0
RESETS
NOTE
TCAPEN
BIT 4
0
BIT 3
0
BIT 2
LED
0
f
BUS
COPON
BIT 1
0
MC68HC05PL4
REV 2.0
BIT 0
POR
0