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Computer Operating Properly (COP)
Data Sheet
MC68HLC908QY/QT Family — Rev. 2
58
Computer Operating Properly (COP)
MOTOROLA
The COP counter is a free-running 6-bit counter preceded by the 12-bit system
integration module (SIM) counter. If not cleared by software, the COP counter
overflows and generates an asynchronous reset after 218 –24 or 213 –24
BUSCLKX4 cycles; depending on the state of the COP rate select bit, COPRS, in
configuration register 1. With a 218 –24 BUSCLKX4 cycle overflow option, the
internal 12.8-MHz oscillator gives a COP timeout period of 20.48 ms. Writing any
value to location $FFFF before an overflow occurs prevents a COP reset by
clearing the COP counter and stages 12–5 of the SIM counter.
NOTE:
Service the COP immediately after reset and before entering or after exiting stop
mode to guarantee the maximum time before the first COP counter overflow.
A COP reset pulls the RST pin low (if the RSTEN bit is set in the CONFIG1 register)
for 32
× BUSCLKX4 cycles and sets the COP bit in the reset status register (RSR).
NOTE:
Place COP clearing instructions in the main program and not in an interrupt
subroutine. Such an interrupt subroutine could keep the COP from generating a
reset even while the main program is not working properly.
6.3 I/O Signals
The following paragraphs describe the signals shown in Figure 6-1.
6.3.1 BUSCLKX4
BUSCLKX4 is the oscillator output signal. BUSCLKX4 frequency is equal to the
crystal frequency or the RC-oscillator frequency.
6.3.2 STOP Instruction
The STOP instruction clears the SIM counter.
6.3.3 COPCTL Write
Writing any value to the COP control register (COPCTL) (see 6.4 COP Control Register) clears the COP counter and clears stages 12–5 of the SIM counter.
Reading the COP control register returns the low byte of the reset vector.
6.3.4 Power-On Reset
The power-on reset (POR) circuit in the SIM clears the SIM counter
4096
× BUSCLKX4 cycles after power up.
6.3.5 Internal Reset
An internal reset clears the SIM counter and the COP counter.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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