MC68HC08AZ16 Datasheet, PDF (462/527 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Appendix B: TIMA-6
Functional Description
Functional Description
Figure 1 shows the TIMA structure. The central component of the TIMA
is the 16-bit TIMA counter that can operate as a free-running counter or
a modulo up-counter. The TIMA counter provides the timing reference
for the input capture and output compare functions. The TIMA counter
modulo registers, TAMODH–TAMODL, control the modulo value of the
TIMA counter. Software can read the TIMA counter value at any time
without affecting the counting sequence.
The six TIMA channels are programmable independently as input
capture or output compare channels.
TIMA Counter
Prescaler
The TIMA clock source can be one of the seven prescaler outputs or the
TIMA clock pin, PTD6/TACLK. The prescaler generates seven clock
rates from the internal bus clock. The prescaler select bits, PS[2:0], in
the TIMA status and control register select the TIMA clock source.
Input Capture
5-tima6
MOTOROLA
An input capture function has three basic parts: edge select logic, an
input capture latch, and a 16-bit counter. Two 8-bit registers, which make
up the 16-bit input capture register, are used to latch the value of the
free-running counter after the corresponding input capture edge detector
senses a defined transition. The polarity of the active edge is
programmable. The level transition which triggers the counter transfer is
defined by the corresponding input edge bits (ELSxB and ELSxA in
TASC0 through TASC5 control registers with x referring to the active
channel number). When an active edge occurs on the pin of an input
capture channel, the TIMA latches the contents of the TIMA counter into
the TIMA channel registers, TACHxH–TACHxL. Input captures can
generate TIMA CPU interrupt requests. Software can determine that an
input capture event has occurred by enabling input capture interrupts or
by polling the status flag bit.
The result obtained by an input capture will be two more than the value
of the free-running counter on the rising edge of the internal bus clock
preceding the external transition. This delay is required for internal
synchronization.
Appendix B: TIMA-6
MC68HC08AZ32
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