Computer Operating Properly (COP) Watchdog Function
M68HC11E Family Data Sheet, Rev. 5.1
Freescale Semiconductor
143
PEDGE — Pulse Accumulator Edge Control Bit
DDRA3 — Data Direction for Port A Bit 3
I4/O5 — Input Capture 4/Output Compare Bit
RTR[1:0] — RTI Interrupt Rate Select Bits
These two bits determine the rate at which the RTI system requests interrupts. The RTI system is
driven by an E divided by 213 rate clock that is compensated so it is independent of the timer prescaler.
These two control bits select an additional division factor. Refer to
Table 9-5.9.6 Computer Operating Properly (COP) Watchdog Function
The clocking chain for the COP function, tapped off of the main timer divider chain, is only superficially
related to the main timer system. The CR[1:0] bits in the OPTION register and the NOCOP bit in the
CONFIG register determine the status of the COP function. One additional register, COPRST, is used to
detailed discussion of the COP function.
9.7 Pulse Accumulator
The M68HC11 Family of MCUs has an 8-bit counter that can be configured to operate either as a simple
event counter or for gated time accumulation, depending on the state of the PAMOD bit in the PACTL
register. Refer to the pulse accumulator block diagram,
Figure 9-24. In the event counting mode, the 8-bit
counter is clocked to increasing values by an external pin. The maximum clocking rate for the external
event counting mode is the E clock divided by two. In gated time accumulation mode, a free-running
E-clock divide-by-64 signal drives the 8-bit counter, but only while the external PAI pin is activated. Refer
to
Table 9-6. The pulse accumulator counter can be read or written at any time.
Pulse accumulator control bits are also located within two timer registers, TMSK2 and TFLG2, as
described in the following paragraphs.
Table 9-6. Pulse Accumulator Timing
Crystal
Frequency
E Clock
Cycle Time
E
÷ 64
PACNT
Overflow
4.0 MHz
1 MHz
1000 ns
64
s
16.384 ms
8.0 MHz
2 MHz
500 ns
32
s
8.192 ms
12.0 MHz
3 MHz
333 ns
21.33
s
5.461 ms