mc68hc908kx8 Freescale Semiconductor, Inc, mc68hc908kx8 Datasheet - Page 52

• Manufacturer Part Number: mc68hc908kx8
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

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 2
cycles, depending on the state of the COP rate select bit, COPRS, in the configuration register. With a
2
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.
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
5.4 I/O Signals
The following paragraphs describe the signals shown in
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.
52
18
–2
4
CGMXCLK cycle overflow option, a 4.9152-MHz CGMXCLK frequency gives a COP timeout
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.
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.
MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 Data Sheet, Rev. 2.1
NOTE
NOTE
Figure
5-1.
TST
.
13
–2
4
or 2
18
Freescale Semiconductor
–2
4
CGMXCLK