MC908KX2MDWE Datasheet, PDF (52/210 Pages) Freescale Semiconductor, Inc – High-performance M68HC08 architecture, Fully upward-compatible object code with M6805, M146805, and M68HC05 Families

Computer Operating Properly Module (COP)
5.3 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 2¹³â€“2⁴ or 2¹⁸–2⁴ CGMXCLK
cycles, depending on the state of the COP rate select bit, COPRS, in the configuration register. With a
2¹⁸–2⁴ CGMXCLK cycle overflow option, a 4.9152-MHz CGMXCLK frequency 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 5–12 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 an internal reset for 64 CGMXCLK cycles and sets the COP bit in the system integration
module (SIM) reset status register (SRSR).
In monitor mode, the COP is disabled if the IRQ1 pin is held at V_TST.
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.
5.4 I/O Signals
The following paragraphs describe the signals shown in Figure 5-1.
5.4.1 CGMXCLK
CGMXCLK is the internal clock generator (ICG) module’s oscillator output signal. CGMXCLK is selected
from either the internal clock source or the external crystal.
5.4.2 STOP Instruction
The STOP instruction clears the COP prescaler.
5.4.3 COPCTL Write
Writing any value to the COP control register (COPCTL) clears the COP counter and clears stages 12–5
of the COP prescaler. Reading the COP control register returns the low byte of the reset vector.
5.4.4 Power-On Reset
The power-on reset (POR) circuit clears the COP prescaler 4096 CGMXCLK cycles after power-up.
5.4.5 Internal Reset
An internal reset clears the COP prescaler and the COP counter.
MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 Data Sheet, Rev. 2.1
52
Freescale Semiconductor