mc68hc11d0cfn2 Freescale Semiconductor, Inc, mc68hc11d0cfn2 Datasheet - Page 95

• Manufacturer Part Number: mc68hc11d0cfn2
• Description: M68hc11 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

8.1 Introduction
MC68HC711D3 — Rev. 2
MOTOROLA
Data Sheet — MC68HC711D3
The M68HC11 timing system is composed of five clock divider chains. The main
clock divider chain includes a 16-bit free-running counter, which is driven by a
programmable prescaler. The main timer's programmable prescaler provides one
of the four clocking rates to drive the 16-bit counter. Two prescaler control bits
select the prescale rate.
The prescaler output divides the system clock by 1, 4, 8, or 16. Taps off of this main
clocking chain drive circuitry that generates the slower clocks used by the pulse
accumulator, the real-time interrupt (RTI), and the computer operating properly
(COP) watchdog subsystems. Refer to
All main timer system activities are referenced to this free-running counter. The
counter begins incrementing from $0000 as the microcontroller unit (MCU) comes
out of reset, and continues to the maximum count, $FFFF. At the maximum count,
the counter rolls over to $0000, sets an overflow flag, and continues to increment.
As long as the MCU is running in a normal operating mode, there is no way to reset,
change, or interrupt the counting. The capture/compare subsystem features three
input capture channels, four output compare channels, and one channel that can
be selected to perform either input capture or output compare. Each of the three
input capture functions has its own 16-bit input capture register (time capture latch)
and each of the output compare functions has its own 16-bit compare register. All
timer functions, including the timer overflow and RTI have their own interrupt
controls and separate interrupt vectors.
The pulse accumulator contains an 8-bit counter and edge select logic. The pulse
accumulator can operate in either event counting or gated time accumulation
modes. During event counting mode, the pulse accumulator's 8-bit counter
increments when a specified edge is detected on an input signal. During gated time
accumulation mode, an internal clock source increments the 8-bit counter while an
input signal has a predetermined logic level.
RTI is a programmable periodic interrupt circuit that permits pacing the execution
of software routines by selecting one of four interrupt rates.
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Programmable Timer
Section 8. Programmable Timer
Figure
8-1.
Data Sheet
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