MC908AZ60ACFUER Datasheet, PDF (163/414 Pages) Freescale Semiconductor, Inc – To provide the most up-to-date information, the revision of our documents on the World Wide Web will be the most current. Your printed copy may be an earlier revision. To verify you have the latest information available, refer to:

Chapter 15
Computer Operating Properly (COP)
15.1 Introduction
The COP module contains a free-running counter that generates a reset if allowed to overflow. The COP
module helps software recover from runaway code. Prevent a COP reset by periodically clearing the COP
counter.
15.2 Functional Description
The COP counter is a free-running 6-bit counter preceded by a 12-bit prescaler. If not cleared by software,
the COP counter overflows and generates an asynchronous reset after 2¹³ – 2⁴ or 2¹⁸ – 2⁴ CGMXCLK
cycles, depending on the state of the COP long timeout bit, COPL, in the CONFIG-1. When COPL = 0, a
4.9152-MHz crystal gives a COP timeout period of 53.3 ms. Writing any value to location $FFFF before
an overflow occurs prevents a COP reset by clearing the COP counter and stages 4–12 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 for 32 CGMXCLK cycles and sets the COP bit in the reset status
register (RSR).
In monitor mode, the COP is disabled if the RST pin or the IRQ pin is held at V_Hi. During the break
state, V_Hi on the RST pin disables the COP.
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.
15.3 I/O Signals
The following paragraphs describe the signals shown in Figure 15-1.
MC68HC908AZ60A • MC68HC908AS60A • MC68HC908AS60E Data Sheet, Rev. 6
Freescale Semiconductor
163