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14. Frequency programming
Figure 15. Relation between f
The
frequency
synthesiser
controlled by the frequency word in the
configuration registers. There are two
frequency words, A and B, which can be
programmed to two different frequencies.
One of the frequency words can be used
for RX (local oscillator frequency) and the
other for TX (transmitting frequency, f
This makes it possible to switch very fast
between RX mode and TX mode. They
can also be used for RX (or TX) on two
different
channels.
control bit performs selection of frequency
word A or B.
The frequency word, FREQ, is 24 bits (3
bytes)
located
FREQ_2A:FREQ_1A:FREQ_0A
FREQ_2B:FREQ_1B:FREQ_0B for the A
and B word, respectively.
The frequency word FREQ can be
calculated from:
+
FREQ
FSEP
=
⋅
f
f
VCO
ref
where TXDATA is 0 or 1 in transmit mode
depending
on
the
transmitted on DIO. In receive mode
TXDATA is always 0.
The reference frequency f
oscillator clock divided by PLL.REFDIV, a
RX mode:
f
f
(low-side)
RF
LO
(Receive frequency)
f
IF
TX mode:
f
f
0
RF
(Lower FSK
(Center frequency)
frequency)
f
sep
(PLL)
is
).
0
The
MAIN.F_REG
in
and
⋅
+
TXDATA
8192
,
16384
data
bit
to
be
is the crystal
ref
SWRS048A
f
vco
f
(high-side)
LO
f
IF
f
f
1
vco
(Upper FSK
frequency)
, f
, and LO frequency
vco
if
number between 2 and 14 that should be
chosen such that:
1.0 MHz ≤ f
ref
Thus, the reference frequency f
=
f
ref
REFDIV
f
is the Local Oscillator (LO) frequency
VCO
in receive mode, and the f
transmit mode (lower FSK frequency). The
LO frequency must be f
giving low-side or high side LO injection
respectively. Note that the data on DIO will
be inverted if high-side LO is used.
The upper FSK transmit frequency is
given by:
f
= f
1
0
where the frequency separation f
by
the
11
bit
(FSEP1:FSEP0):
=
f
f
sep
ref
Clearing
PLL.ALARM_DISABLE
enable generation of the frequency alarm
bits PLL.ALARM_H and PLL.ALARM_L.
These bits indicate that the frequency
CC1000
≤ 2.46 MHz
is:
ref
f
xosc
frequency in
0
– f
or f
+ f
RF
IF
RF
IF
+ f
,
sep
is set
sep
separation
word
FSEP
⋅
16384
will
Page 23 of 55
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