MC68HC908GT16_07 Datasheet, PDF (62/292 Pages) Freescale Semiconductor, Inc – Microcontrollers

Computer Operating Properly (COP) Module
The COP counter is a free-running 6-bit counter preceded by a 12-bit prescaler counter. If not cleared by
software, the COP counter overflows and generates an asynchronous reset after 262,128 or 8176
COPCLK cycles, depending on the state of the COP rate select bit, COPRS, in the configuration register.
With a 8176 COPCLK cycle overflow option, a 32.768-kHz crystal gives a COP timeout period of 250 ms.
Writing any value to location $FFFF before an overflow occurs prevents a COP reset by clearing the COP
counter and stages 12 through 5 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 COPCLK cycles and sets the COP bit in the reset status register
(RSR).
In monitor mode, the COP is disabled if the RST pin or the IRQ1 is held at V_TST. During the break state,
V_TST 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.
5.3 I/O Signals
The following paragraphs describe the signals shown in Figure 5-1.
5.3.1 COPCLK
COPCLK is a clock generated by the clock selection circuit in the internal clock generator (ICG). See 7.3.5
Clock Selection Circuit for more details.
5.3.2 STOP Instruction
The STOP instruction clears the COP prescaler.
5.3.3 COPCTL Write
Writing any value to the COP control register (COPCTL) (see 5.4 COP Control Register) clears the COP
counter and clears bits 12 through 5 of the prescaler. Reading the COP control register returns the low
byte of the reset vector.
5.3.4 Power-On Reset
The power-on reset (POR) circuit clears the COP prescaler 4096 CGMXCLK cycles after power-up.
5.3.5 Internal Reset
An internal reset clears the COP prescaler and the COP counter.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
62
Freescale Semiconductor