MC68HC908RK2 Datasheet, PDF (43/158 Pages) Motorola, Inc – Microcontroller Unit

Chapter 4
Computer Operating Properly Module (COP)
4.1 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.
4.2 Functional Description
CGMXCLK
12-BIT COP PRESCALER
STOP INSTRUCTION
INTERNAL RESET SOURCES
RESET VECTOR FETCH
COPCTL WRITE
COPD FROM CONFIG
RESET
COPCTL WRITE
COPRS FROM CONFIG
6-BIT COP COUNTER
CLEAR COP
COUNTER
RESET
RESET STATUS
REGISTER
Figure 4-1. 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 2¹³ – 2⁴ or 2¹⁸ – 2⁴ CGMXCLK
cycles, depending on the state of the COP rate select bit, COPRS, in the configuration register. When
COPRS = 1, a 4.9152-MHz crystal gives a COP timeout period of 53.3 ms. Writing any value to location
MC68HC908RK2 Data Sheet, Rev. 5.1
Freescale Semiconductor
43