C2510Fx / CC2511Fx
13.1.5.1 High Speed Oscillators
13.1.5.2 System clock speed and radio
Two high speed oscillators are present in the
device:
When the radio is to be used the system must
run on HS XOSC. The RF part will be
unaffected by the CLKCON.CLKSPD setting.
There is however parts of the RF core that
runs on the system clock affected by and this
will cause limitations in manageable data rates
in RF link. These limitations are summarized in
Table 49 below. Note that these numbers does
not apply for FEC usage. Using FEC requires
CLKCON.CLKSPD to be 000.
• High speed crystal oscillator (24 – 27
MHz for CC2510Fx and 48 MHz for
CC2511Fx)
• High speed RC oscillator (12 – 13.5
MHz for CC2510Fx and 12 MHz for
CC2511Fx)
The high speed crystal oscillator startup time
may be too long for some applications, and the
device can therefore run on the high speed
RCOSC until the crystal oscillator is stable.
The HS RCOSC consumes less power than
the crystal oscillator, but since it is not as
accurate as the crystal oscillator it can not be
used for RF transceiver operation.
CLKCON
CLKSPD
000
Maksimum datarate, kBaud
MSK GFSK 2FSK
500 250 500
001
500
500
500
400
200
100
50
250
250
250
250
200
100
50
500
500
500
400
200
100
50
010
The CLKCON.OSCbit selects the source of the
system clock (high speed crystal oscillator or
high speed RC oscillator). The system clock
will not change clock source before the
selected clock source is stable (indicated by
SLEEP.XOSC_STBand SLEEP.HFRC_STB).
011
100
101
110
111
The oscillator not selected as the system clock
source, will be set in power-down mode by
setting SLEEP.OSC_PDto 1 (the default state).
Thus the HS RCOSC may be turned off when
the high speed crystal oscillator has been
selected as system clock source and vice
versa. When SLEEP.OSC_PD is 0, both
oscillators are powered up and running. Be
aware that SLEEP.OSC_PD is cleared if the
CLKCON.OSCbit is toggled.
Table 49: System clock speed VS data rate
13.1.5.3 Low Speed Oscillators (32 kHz clock
source)
Two low speed oscillators are present in the
device:
• Low speed crystal oscillator (32.768
kHz)
When the high speed crystal oscillator is
selected
as
system
clock
source
• Low power RC oscillator (32 – 36 kHz
for CC2510Fx and 32 kHz for CC2511Fx)
(CLKCON.OSCis set to 0), the HS RCOSC will
be calibrated once. If SLEEP.OSC_PD=0, the
HS RCOSC will run on the calibrated value
once the calibration is completed (see Table
The low speed crystal oscillator is designed to
operate at 32.768 kHz and provide a stable
clock signal for systems requiring time
accuracy. The low power RC oscillator run at
fXOSC / 750 for CC2510Fx and fXOSC / 1500 for
CC2511Fx, when calibrated. The calibration can
only take place when the high speed crystal
oscillator is enabled and stable. The low power
RC oscillator should be used to reduce cost
and power consumption compared to the
32.768 kHz crystal oscillator solution. The two
low speed oscillators can not be operated
simultaneously.
15
for
initial
calibration
time).
If
SLEEP.OSC_PD=1, the HS RCOSC will be
turned off after calibration, but the calibration
value will be stored and used when the HS
RCOSC is started again. In order to calibrate
the HS RCOSC regularly (if so found
necessary based on the drift parameters listed
in Table 15) one should switch between using
the HS RCOSC and the high speed crystal
oscillator as system clock source.
If CLKCON.OSC is set to 0 when entering
PM{1-3}, the HS RCOSC will be calibrated
once when returning to active mode.
By default, after a reset, the low power RC
oscillator is enabled and selected as the 32
kHz clock source. The RC oscillator consumes
less power, but is less accurate than the
SWRS055D
Page 78 of 243
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