Chapter 5 Resets, Interrupts, and System Configuration
MC9S08AC16 Series Data Sheet, Rev. 9
64
Freescale Semiconductor
Computer operating properly (COP) timer
Illegal opcode detect
Illegal address detect
Background debug forced reset
The reset pin (RESET)
Clock generator loss of lock and loss of clock reset
Each of these sources, with the exception of the background debug forced reset, has an associated bit in
the system reset status register.
5.4
Computer Operating Properly (COP) Watchdog
The COP watchdog is intended to force a system reset when the application software fails to execute as
expected. To prevent a system reset from the COP timer (when it is enabled), application software must
reset the COP counter periodically. If the application program gets lost and fails to reset the COP counter
before it times out, a system reset is generated to force the system back to a known starting point.
it can be disabled by clearing COPE. The COP counter is reset by writing any value to the address of SRS.
This write does not affect the data in the read-only SRS. Instead, the act of writing to this address is
decoded and sends a reset signal to the COP counter.
information) selects the clock source used for the COP timer. The clock source options are either the bus
clock or an internal 1-kHz clock source. With each clock source, there is an associated short and long
time-out controlled by COPT in SOPT.
Table 5-1 summaries the control functions of the COPCLKS and
COPT bits. The COP watchdog defaults to operation from the bus clock source and the associated long
time-out (218 cycles).
Even if the application will use the reset default settings of COPE, COPCLKS, and COPT, the user must
write to the write-once SOPT and SOPT2 registers during reset initialization to lock in the settings. That
way, they cannot be changed accidentally if the application program gets lost. The initial writes to SOPT
and SOPT2 will reset the COP counter.
Table 5-1. COP Configuration Options
Control Bits
Clock Source
COP Overflow Count
COPCLKS
COPT
00
~1 kHz
25 cycles (32 ms)1
1 Values are shown in this column based on t
RTI =1 ms. See tRTI in the appendix
01
~1 kHz
28 cycles (256 ms)1
10
Bus
213 cycles
11
Bus
218 cycles