
Computer Operating Properly (COP) Module
Power-On Reset (POR) and Computer Operating Properly (COP), Rev. 4
Freescale Semiconductor
7-5
For the digital power supply the POR trip point is:
This means, as long as the analog power supply is below 2.8V, the POR_3p3 will be high. When
the analog power supply exceeds 2.9V the POR_3p3 output will be low. Respectively, for the
digital power supply, when the digital power supply is below 1.62V the POR_1p8 output will be
high. When the digital power supply is above 1.7V the POR_1p8 output will be low.
7.5 Computer Operating Properly (COP) Module
The Computer Operating Properly (COP) module is used to help software recover from runaway
code. The COP is a free-running down counter, once enabled is designed to generate a Reset
upon reaching zero. Software must periodically service the COP in order to clear the counter and
prevent a reset.
7.5.1 COP Functional Description
When the COP is enabled, each positive edge of OSCCLK will cause the counter to decrement by
one. If the count reaches a value of $0000, then the COP_RST signal is asserted and the chip is
reset. In order for the CPU to show it is operating properly, it must perform a service routine prior
to the count reaching $0000. The service routine consists of writing $5555 followed by $AAAA
to COPCTR.
7.5.2 Time-Out Specifications
The COP uses a 16-bit counter, being clocked by the crystal oscillator clock prescaled by 128.
Table 7-1
presents the range of time-out values supported as a function of oscillator frequency.
For a crystal operating at 4MHz the clock to the COP counter will be 31.25KHz. The value of the
COPTO register can be programmed from 1 to 65535 giving a time-out period range from 32μsec
minimum to 2.1sec maximum.
Absolute Minimum
1.62V
Nominal
1.66V
Absolute Maximum
1.7V
Table 7-1. COP Time-out Ranges as a Function of Oscillator Frequency
CT
2 MHz
64 μsec
4.2 sec
4MHz
32 μsec
2.1 sec
$0000
$FFFF