MC68HC908MR8 Datasheet, PDF (204/372 Pages) Motorola, Inc – Microcontrollers

Timer Interface A (TIMA)
11.4 Functional Description
Figure 11-1 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 two TIMA channels are programmable independently as input
capture or output compare channels.
11.4.1 TIMA Counter Prescaler
The TIMA clock source can be one of the seven prescaler outputs or the
TIMA clock pin, PTB2/TCLKA. 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.
11.4.2 Input Capture
An input capture function has three basic parts:
1. Edge select logic
2. Input capture latch
3. 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 the TASC0 and 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
Technical Data
204
Timer Interface A (TIMA)
MC68HC908MR8 — Rev 4.1
Freescale Semiconductor