MC68HC711G5 MOTOROLA [Motorola, Inc], MC68HC711G5 Datasheet - Page 71

• Manufacturer Part Number: MC68HC711G5
• Description: High-density Complementary Metal Oxide Semiconductor (HCMOS) Microcontroller
• Manufacturer: MOTOROLA [Motorola, Inc]

SECTION 6
PROGRAMMABLE TIMER, REAL TIME INTERRUPT AND PULSE
ACCUMULATOR
This section describes the 16-bit programmable timer, the real time interrupt and the pulse
accumulator system.
In order to reduce the overhead required to service interrupts, the three timer overflows and the other
twelve timer functions each have their own interrupt vector, and each of these interrupts is
independently maskable.
6.1
PROGRAMMABLE TIMER
The timer system on the MC68HC11G5 has been derived from the original MC68HC11A8 timer.
There are four fixed output compares (OC), three fixed input captures (IC) and three programmable
input captures/output compares (IC/OC).
Secondly, there are two separate “time-of-day” type 16-bit free-running counters, each with its own
prescaler. The first counter is associated with the four fixed output compares and two of the
programmable input capture/output compares. The second counter is associated with the three
fixed input captures and one programmable input capture/output compare.
6.1.1
Counters
The two 16-bit counters (TCNT1 and TCNT2) are clocked by the outputs of separate 3-stage
prescalers (divide by 1, 2, 4, or 8) which are in turn driven by the MCU E-clock. (Note that these
prescaler values have been changed from the original MC68HC11A8 to include divide-by-2 and to
exclude divide-by-16.) The second counter can also be driven by an external clock instead of the
internal clock. An external clock cannot be used with counter 1 because this counter chain is also
used to time the real time interrupt and the COP circuit.
In addition, counter 2 can be cleared by software. This is accomplished by writing any value to the
counter register. This forces a hardware reset of the counter, regardless of the value written. This
feature is not available on counter 1 because counter 1 is also used to time the real time interrupt
and the COP circuit.
MC68HC11G5
PROGRAMMABLE TIMER
MOTOROLA
6-1