mc68hc908qf4 Freescale Semiconductor, Inc, mc68hc908qf4 Datasheet - Page 56

• Manufacturer Part Number: mc68hc908qf4
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Computer Operating Properly (COP)
6.3 I/O Signals
6.3.1 BUSCLKX4
6.3.2 STOP Instruction
6.3.3 COPCTL Write
6.3.4 Power-On Reset
6.3.5 Internal Reset
Data Sheet
56
NOTE:
NOTE:
The COP counter is a free-running 6-bit counter preceded by the 12-bit system
integration module (SIM) counter. If not cleared by software, the COP counter
overflows and generates an asynchronous reset after 2
BUSCLKX4 cycles; depending on the state of the COP rate select bit, COPRS, in
configuration register 1. With a 2
internal 12.8-MHz oscillator gives a COP timeout period of 20.48 ms. Writing any
value to location $FFFF before an overflow occurs prevents a COP reset by
clearing the COP counter and stages 12–5 of the SIM counter.
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 (if the RSTEN bit is set in the CONFIG1 register)
for 32 × BUSCLKX4 cycles and sets the COP bit in the reset status register (RSR).
See
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.
The following paragraphs describe the signals shown in
BUSCLKX4 is the oscillator output signal. BUSCLKX4 frequency is equal to the
crystal frequency or the RC-oscillator frequency.
The STOP instruction clears the SIM counter.
Writing any value to the COP control register (COPCTL) (see
Register) clears the COP counter and clears stages 12–5 of the SIM counter.
Reading the COP control register returns the low byte of the reset vector.
The power-on reset (POR) circuit in the SIM clears the SIM counter
4096 × BUSCLKX4 cycles after power up.
An internal reset clears the SIM counter and the COP counter.
14.8.1 SIM Reset Status
Freescale Semiconductor, Inc.
For More Information On This Product,
Computer Operating Properly (COP)
Go to: www.freescale.com
Register.
18
– 2
4
BUSCLKX4 cycle overflow option, the
18
Figure
MC68HC908QF4 — Rev. 1.0
– 2
4
6.4 COP Control
or 2
6-1.
13
– 2
MOTOROLA
4