MC68HC11P2 Datasheet, PDF (137/268 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Technical Data — MC68HC11P2
Section 8. Timing System
8.1 Contents
8.2 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
8.3 Timer structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
8.4 Input capture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
8.5 Output compare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
8.6 Real-time interrupt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
8.7 Computer operating properly watchdog function . . . . . . . 157
8.8 Pulse accumulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
8.9 Pulse-width modulation (PWM) timer . . . . . . . . . . . . . . . . . 162
8.2 Introduction
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
from this main clocking chain drive circuitry generate the slower clocks
used by the pulse accumulator, the real-time interrupt (RTI), and the
computer operating properly (COP) watchdog subsystems, which are
also described in this section. Refer to Figure 8-1.
All main timer system activities are referenced to this free-running
MC68HC11P2 — Rev 1.0
Timing System
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Technical Data