MC68HC05F8 Datasheet, PDF (49/126 Pages) Motorola, Inc – High-density complementary metal oxide semiconductor(HCMOS) microcontroller unit

Freescale Semiconductor, Inc.
6
TIMERS
6.1
TIMER A - PROGRAMMABLE TIMER
The timer consists of a 16-bit free-running counter driven by a fixed divide-by-four prescaler. This
timer can be used for many purposes, including input waveform measurements while
6
simultaneously generating an output waveform. Pulse widths can vary from several microseconds
to many seconds. Figure 6-1 shows a block diagram for the Programmable Timer.
Because the timer has a 16-bit architecture, the I/O registers for the input capture and output
compare functions are pairs of 8-bit registers (high byte and low byte). Generally, assessing the
low byte of a specific timer function allows full control of that function. However, an access of the
high byte inhibits that specific timer function until the low byte is also accessed.
Note:
The I bit in the condition code register should be set while manipulating both the high
and low byte register of a specific timer function to ensure that an interrupt does not
occur.
Ten 8-bit registers are associated with the programmable timer.
– Timer Control Register (TCR)
– Timer Status Register (TSR)
– Input Capture Register
– Output Compare Register
– Counter Register
– Alternate Counter Register
$18
$19
High byte - $1A, Low byte - $1B
High byte - $1C, Low byte - $1D
High byte - $1E, Low byte - $1F
High byte - $20, Low byte - $21
A description of each register is provided in the following paragraphs.
6.1.1 Counter
– Timer A Counter
– Timer A Alternate Counter
High byte - $1E, Low byte - $1F
High byte - $20, Low byte - $21
MC68HC05F8
TIMERS
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TPG
MOTOROLA
6-1