mc68hc08qa24 Freescale Semiconductor, Inc, mc68hc08qa24 Datasheet - Page 317

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

21.4 Functional Description
21.4.1 TIMB Counter Prescaler
21.4.2 Input Capture
MC68HC08QA24
Freescale Semiconductor
Figure 21-1
TIMB is the 16-bit TIMB counter that can operate as a free-running
counter or a modulo up-counter. The TIMB counter provides the timing
reference for the input capture and output compare functions. The TIMB
counter modulo registers, TBMODH–TBMODL, control the modulo
value of the TIMB counter. Software can read the TIMB counter value at
any time without affecting the counting sequence.
The two TIMB channels are programmable independently as input
capture or output compare channels.
The TIMB clock source can be one of the seven prescaler outputs or the
TIMB clock pin, PTF2/TBCLK. The prescaler generates seven clock
rates from the internal bus clock. The prescaler select bits, PS[2:0], in
the TIMB status and control register select the TIMB 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 TBSC0 through TBSC1 control registers
with x referring to the active channel number). When an active edge
occurs on the pin of an input capture channel, the TIMB latches the
contents of the TIMB counter into the TIMB channel registers,
TCHxH–TCHxL. Input captures can generate TIMB 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 TIMB structure. The central component of the
Timer Interface B (TIMB)
Timer Interface B (TIMB)
Technical Data
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