C2510Fx / CC2511Fx
13.9 8-bit Timers, Timer 3 and Timer 4
Timer 3 and Timer 4 are two 8-bit timers which
supports typical timer/counter functions such
as output compare and PWM functions. The
timers have two independent compare
channels each and use one I/O pin per
channel.
The features of Timer 3/4 are as follows:
•
Two compare channels
•
Set, clear, or toggle output compare
•
Free-running,
modulo,
down,
up/down counter operation
or
speed RC oscillator is used as system clock
source, the highest clock frequency used by
Timer 3/4 is
f
XOSC
/2 for
CC2510Fx
and 12 MHz
for
CC2511Fx
, given that the HS RCOSC has
been calibrated.
The counter operates as either a free-running
counter, a modulo counter, a down counter, or
as an up/down counter for use in centre-
aligned PWM.
It is possible to read the 8-bit counter value
through the SFR
Writing a 1 to
will reset the 8-bit
counter.
The counter may produce an interrupt request
when the terminal count value (overflow) is
reached (see Section 13.9.2.1 – Section
counter with the
bit. The
counter is started when a 1 is written to
If a 0 is written to
the counter halts at its
present value.
13.9.2
Timer 3/4 Operation
•
Clock prescaler for divide by 1, 2, 4, 8,
16, 32, 64, 128
•
Interrupt request generation on compare
and when reaching the terminal count
value
•
DMA trigger function
Note: In the following sections, an
n
in the
register name represent the channel
number 0 or 1 if nothing else is stated. An
x
in the register name refers to the timer
number, 3 or 4
13.9.1
8-bit Timer Counter
Both timers consist of an 8-bit counter that
increments or decrements at each active clock
edge. The frequency of the active clock edges
is
given
by
and
is used to set
the timer tick speed. The timer tick speed will
vary from 203.125 kHz to 26 MHz for
CC2510Fx
and 187.5 kHz to 24 MHz for
CC2511Fx
(given
the use of a 26 MHz or 48 MHz crystal
respectively). Note that the clock speed of the
system clock is not affected by the
setting. The timer tick speed is further divided
in Timer 3/4 by the prescaler value set by
This prescaler value can be 1,
2, 4, 8, 16, 32, 64, or 128. Thus the lowest
clock frequency used by Timer 3/4 is 1.587
kHz and the highest is 26 MHz when a 26
MHz crystal oscillator is used as system clock
source (
CC2510Fx
). The lowest clock frequency
used by Timer 3/4 is 1.465 kHz and the
highest is 24 MHz for
CC2511Fx
. When the high
In general, the control register
is used
to control the timer operation. The timer
modes are described in the following four
sections.
13.9.2.1 Free-running Mode
In free-running mode the counter starts from
0x00 and increments at each active clock
edge. When the counter reaches the terminal
count value 0xFF (overflow), the counter is
loaded with 0x00 and continues incrementing
its value as shown in Figure 34. When 0xFF is
reached, the
flag is set. The
flag is only asserted if the
corresponding
interrupt
mask
bit
is set. An interrupt request is
generated when both
and
are set to 1. The free-running
mode can be used to generate independent
time intervals and output signal frequencies.
SWRS055D
Page 129 of 243
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