mc68hc08qa24 Freescale Semiconductor, Inc, mc68hc08qa24 Datasheet - Page 291

• Manufacturer Part Number: mc68hc08qa24
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

20.4 Functional Description
20.4.1 TIMA Counter Prescaler
20.4.2 Input Capture
MC68HC08QA24
Freescale Semiconductor
Figure 20-1
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 two TIMA channels are programmable independently as input
capture or output compare channels.
The TIMA clock source can be one of the seven prescaler outputs or the
TIMA clock pin, PTF3/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.
An input capture function has three basic parts:
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–TASC1 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, TCHxH–TCHxL. 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.
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Edge select logic
Input capture latch
16-bit counter
shows the TIMA structure. The central component of the
Timer Interface A (TIMA)
Timer Interface A (TIMA)
Technical Data
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