MC68HC908GR16 Datasheet, PDF (86/310 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Computer Operating Properly (COP) Module
NOTE:
NOTE:
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 2¹⁸ – 2⁴ or 2¹³ – 2⁴ CGMXCLK cycles, depending on the
state of the COP rate select bit, COPRS, in the configuration register. With a
2¹³ – 2⁴ CGMXCLK cycle overflow option, 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 12–5 of the
prescaler.
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 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.
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.
6.3 I/O Signals
The following paragraphs describe the signals shown in Figure 6-1.
6.3.1 CGMXCLK
CGMXCLK is the crystal oscillator output signal. CGMXCLK frequency is equal to
the crystal frequency.
6.3.2 STOP Instruction
The STOP instruction clears the COP prescaler.
6.3.3 COPCTL Write
Writing any value to the COP control register (COPCTL) clears the COP counter
and clears bits 12–5 of the prescaler. Reading the COP control register returns the
low byte of the reset vector. See 6.4 COP Control Register.
6.3.4 Power-On Reset
The power-on reset (POR) circuit clears the COP prescaler 4096 CGMXCLK
cycles after power-up.
Data Sheet
86
Computer Operating Properly (COP) Module
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MC68HC908GR16 — Rev. 1.0
MOTOROLA