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Chapter 8 S12 Clock, Reset and Power Management Unit (S12CPMU_UHV_V6)
MC9S12ZVM Family Reference Manual Rev. 1.3
Freescale Semiconductor
301
8.5.5
Computer Operating Properly Watchdog (COP) Reset
The COP (free running watchdog timer) enables the user to check that a program is running and
sequencing properly. When the COP is being used, software is responsible for keeping the COP from
timing out. If the COP times out it is an indication that the software is no longer being executed in the
intended sequence; thus COP reset is generated.
The clock source for the COP is either ACLK, IRCCLK or OSCCLK depending on the setting of the
COPOSCSEL0 and COPOSCSEL1 bit.
Depending on the COP configuration there might be a significant latency time until COP is active again
after exit from Stop Mode due to clock domain crossing synchronization. This latency time occurs if COP
clock source is ACLK and the CSAD bit is set (please refer to CSAD bit description for details).
gives an overview of the COP condition (run, static) in Stop Mode depending on legal
configuration and status bit settings:
Table 8-34. COP condition (run, static) in Stop Mode
Three control bits in the CPMUCOP register allow selection of seven COP time-out periods.
When COP is enabled, the program must write $55 and $AA (in this order) to the CPMUARMCOP
register during the selected time-out period. Once this is done, the COP time-out period is restarted. If the
program fails to do this and the COP times out, a COP reset is generated. Also, if any value other than $55
or $AA is written, a COP reset is generated.
COPOSCSEL1 CSAD PSTP
PCE
COPOSCSEL0
OSCE
UPOSC
COP counter behavior in Stop Mode
(clock source)
1
0
x
x
x
x
x
Run (ACLK)
1
1
x
x
x
x
x
Static (ACLK)
0
x
1
1
1
1
1
Run (OSCCLK)
0
x
1
1
0
0
x
Static (IRCCLK)
0
x
1
1
0
1
x
Static (IRCCLK)
0
x
1
0
0
x
x
Static (IRCCLK)
0
x
1
0
1
1
1
Static (OSCCLK)
0
x
0
1
1
1
1
Static (OSCCLK)
0
x
0
1
0
1
x
Static (IRCCLK)
0
x
0
1
0
0
0
Static (IRCCLK)
0
x
0
0
1
1
1
Satic (OSCCLK)
0
x
0
0
0
1
1
Static (IRCCLK)
0
x
0
0
0
1
0
Static (IRCCLK)
0
x
0
0
0
0
0
Static (IRCCLK)