M68HC08 datasheet(48/188 Pages) FREESCALE

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Computer Operating Properly Module (COP)

Data Sheet

MC68HC908RF2 — Rev. 4.0

Computer Operating Properly Module (COP)

MOTOROLA

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 $FFFF before an overflow occurs prevents a COP reset by

clearing the COP counter and stages 5 through 12 of the prescaler.

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 SIM reset status register (SRSR).

In monitor mode, the COP is disabled if the RST pin or the IRQ pin is held at VTST.

During the break state, VTST 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.

4.3 I/O Signals

The following paragraphs describe the signals shown in Figure 4-1.

4.3.1 CGMXCLK

CGMXCLK is the oscillator output signal. See 6.3.5 Clock Selection Circuit for a

description of CGMXCLK.

4.3.2 STOP Instruction

The STOP instruction clears the COP prescaler.

4.3.3 COPCTL Write

Writing any value to the COP control register (COPCTL) (see 4.4 COP Control

prescaler. Reading the COP control register returns the reset vector.

4.3.4 Power-On Reset

The power-on reset (POR) circuit clears the COP prescaler 4096 CGMXCLK

cycles after power-up.

4.3.5 Internal Reset

An internal reset clears the COP prescaler and the COP counter.

Freescale Semiconductor, Inc.

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M68HC08 Datasheet(PDF) 48 Page - Freescale Semiconductor, Inc