MOTOROLA
4-2
MC68HC05T16
RESETS AND INTERRUPTS
4
4.1.3
Computer Operating Properly (COP) Reset
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:
COP time-out is prevented by periodically writing a ‘0’ to bit 0 of address $FFF0.
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.
Table 4-1 Reset Action on Internal Circuit
DEFAULT CONDITIONS AFTER RESET
1
Timer prescaler reset to zero state
2
Timer counter configures to $FFFC
3
All timer interrupt enable bits cleared (ICIE, OC0IE, OC1IE, and TOVFIE) to disable timer interrupt
4
All data direction registers cleared to zero (default to inputs)
5
Port E and port F configured as general purpose I/O ports
6
Configure stack pointer to $00FF
7
Force internal address bus to the address of reset vector ($FFFE)
8
Set interrupt mask bit (I bit) in condition code register to logic one
9
Clear Stop latch
10
Clear Wait latch
11
Clear all interrupt enable bits
12
COP watchdog timer reset
13
COP watchdog disabled
14
Initialize M-Bus registers
15
Initialize PWM registers
16
Initialize PAC registers
17
OSD disabled, all registers initialized to default values
Listed numbers do not represent order of occurrence.
TPG
30
Содержание MC68HC05T16
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