mc68hc908ey16a Freescale Semiconductor, Inc, mc68hc908ey16a Datasheet - Page 69

• Manufacturer Part Number: mc68hc908ey16a
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Chapter 6
Computer Operating Properly
6.1 Introduction
The computer operating properly (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.
6.2 Functional Description
SIM MODULE
12-BIT SIM COUNTER
SIM RESET CIRCUIT
BUSCLKX4
RESET STATUS REGISTER
(1)
INTERNAL RESET SOURCES
RESET VECTOR FETCH
COPCTL WRITE
COP CLOCK
COP MODULE
6-BIT COP COUNTER
COPEN (FROM SIM)
COPD (FROM CONFIG1)
CLEAR
RESET
COP COUNTER
COPCTL WRITE
COP RATE SELECT
(COPRS FROM CONFIG1)
1. See
Chapter 14 System Integration Module (SIM)
for more details.
Figure 6-1. COP Block Diagram
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 8176 or 262,128 CGMXCLK
cycles, depending on the state of the COP rate select bit, COPRS, in the CONFIG1. When COPRS = 0,
a 4.9152-MHz crystal gives a COP timeout period of 53.3 ms. Writing any value to location $FFFF before
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 1
Freescale Semiconductor
69