MC68HC908MR8 Datasheet, PDF (229/372 Pages) Motorola, Inc – Microcontrollers

Timer Interface B (TIMB)
Functional Description
respond to this event at a later time and determine the actual time of the
event. However, this must be done prior to another input capture on the
same pin; otherwise, the previous time value will be lost.
By recording the times for successive edges on an incoming signal,
software can determine the period and/or pulse width of the signal. To
measure a period, two successive edges of the same polarity are
captured. To measure a pulse width, two alternate polarity edges are
captured. Software should track the overflows at the 16-bit module
counter to extend its range.
Another use for the input capture function is to establish a time
reference. In this case, an input capture function is used in conjunction
with an output compare function. For example, to activate an output
signal a specified number of clock cycles after detecting an input event
(edge), use the input capture function to record the time at which the
edge occurred. A number corresponding to the desired delay is added to
this captured value and stored to an output compare register (see
12.10.5 TIMB Channel Registers). Because both input captures and
output compares are referenced to the same 16-bit modulo counter, the
delay can be controlled to the resolution of the counter independent of
software latencies.
NOTE: Reset does not affect the contents of the input capture channel register
(TBCHxH–TBCHxL).
MC68HC908MR8 — Rev 4.1
Freescale Semiconductor
Timer Interface B (TIMB)
Technical Data
229