Computer Operating Properly (COP)
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 ICLK cycles and sets the COP bit in the SIM reset status register
(SRSR).
In monitor mode, the COP is disabled if the RST pin or the IRQ1 is held at V
. During the break state,
TST
V
on the RST pin disables the COP.
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.
19.3 I/O Signals
The following paragraphs describe the signals shown in Figure 19-1.
19.3.1 ICLK
ICLK is the internal oscillator output signal. See Chapter 22 Electrical Specifications for ICLK frequency
specification.
19.3.2 STOP Instruction
The STOP instruction clears the COP prescaler.
19.3.3 COPCTL Write
Writing any value to the COP control register (COPCTL) (see 19.4 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.
19.3.4 Power-On Reset
The power-on reset (POR) circuit clears the COP prescaler 4096 ICLK cycles after power-up.
19.3.5 Internal Reset
An internal reset clears the COP prescaler and the COP counter.
19.3.6 Reset Vector Fetch
A reset vector fetch occurs when the vector address appears on the data bus. A reset vector fetch clears
the COP prescaler.
19.3.7 COPD (COP Disable)
The COPD signal reflects the state of the COP disable bit (COPD) in the CONFIG1 register. (See
Figure 19-2 . Configuration Register 1 (CONFIG1).)
MC68HC908AP Family Data Sheet, Rev. 4
284
Freescale Semiconductor
FREESCALE [ Freescale ]
