MC68HC705T16 MOTOROLA [Motorola, Inc], MC68HC705T16 Datasheet - Page 32

• Manufacturer Part Number: MC68HC705T16
• Description: High-density complementary metal oxide semiconductor (HCMOS) microcontroller unit
• Manufacturer: MOTOROLA [Motorola, Inc]

4
4.1.3
The MCU contains a watchdog timer that automatically times out if not reset (cleared) within a
specific amount of time by a program reset sequence.
Note:
If the watchdog timer is allowed to time-out, an internal reset is generated to reset the MCU.
Because the internal reset signal is used, the MCU comes out of a COP reset in the same
operating mode it was in when the COP time-out was generated.
The watchdog timer is initially disabled after a reset, it is enabled by setting the WDOG bit in the
Multi-Function Timer register (writing a ‘1’ to bit 2 of address $1C); see Section 5.2 for more
details. Once enabled, it cannot be disabled by software.
Table 4-1 shows the internal circuit actions on reset, but not necessary in order of occurrence.
MOTOROLA
4-2
Listed numbers do not represent order of occurrence.
10
11
12
13
14
15
16
17
1
2
3
4
5
6
7
8
9
COP time-out is prevented by periodically writing a ‘0’ to bit 0 of address $FFF0.
Computer Operating Properly (COP) Reset
Timer prescaler reset to zero state
Timer counter configures to $FFFC
All timer interrupt enable bits cleared (ICIE, OC0IE, OC1IE, and TOVFIE) to disable timer interrupt
All data direction registers cleared to zero (default to inputs)
Port E and port F configured as general purpose I/O ports
Configure stack pointer to $00FF
Force internal address bus to the address of reset vector ($FFFE)
Set interrupt mask bit (I bit) in condition code register to logic one
Clear Stop latch
Clear Wait latch
Clear all interrupt enable bits
COP watchdog timer reset
COP watchdog disabled
Initialize M-Bus registers
Initialize PWM registers
Initialize PAC registers
OSD disabled, all registers initialized to default values
Table 4-1 Reset Action on Internal Circuit
RESETS AND INTERRUPTS
DEFAULT CONDITIONS AFTER RESET
MC68HC05T16
TPG