MC68HC705C9A_1 Datasheet, PDF (69/157 Pages) Freescale Semiconductor, Inc – General Release Specification

Freescale Semiconductor, Inc.
General Release Specification
Timer Operation
Because the counter is 16 bits long and preceded by a fixed divide-by-4
prescaler, the counter rolls over every 262,144 internal clock cycles.
Timer resolution with a 4-MHz crystal is 2 µs.
8.3.1 Input Capture
The input capture function is a means to record the time at which an
external event occurs. When the input capture circuitry detects an active
edge on the TCAP pin, it latches the contents of the timer registers into
the input capture registers. The polarity of the active edge is
programmable.
Latching values into the input capture registers at successive edges of
the same polarity measures the period of the input signal on the TCAP
pin. Latching values into the input capture registers at successive edges
of opposite polarity measures the pulse width of the signal.
8.3.2 Output Compare
The output compare function is a means of generating an output signal
when the 16-bit counter reaches a selected value. Software writes the
selected value into the output compare registers. On every fourth
internal clock cycle the output compare circuitry compares the value of
the counter to the value written in the output compare registers. When a
match occurs, the timer transfers the programmable output level bit
(OLVL) from the timer control register to the TCMP pin.
The programmer can use the output compare register to measure time
periods, to generate timing delays, or to generate a pulse of specific
duration or a pulse train of specific frequency and duty cycle on the
TCMP pin.
MC68HC705C9A — Rev. 2.0
Capture/Compare Timer
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