9
The demodulator corrects the
processing clock (ADC sampling
clock) frequency around its nominal
value so as to track small changes in
the received signal symbol rate.
20-bit unsigned integer expressed as
f
clk_rx
* 2
20
/ 360MHz.
120 MHz maximum.
20 MHz recommended minimum
REG25 = bits 7-0 (LSB)
REG26 = bits 15 – 8 (MSB)
REG27(3:0) = bits 19 – 16 (MSB)
Nominal symbol
rate
f
symbol rate rx
The demodulator nominal symbol
rate is in the form
f
symbol rate rx
=
f
clk_rx
/ 2
n
where n ranges from 0 (1 sample per
symbol) to 15 (symbol rate =
f
clk_rx
/
32768).
n is defined in REG28(3:0)
Inverse
Modulation Index
1/h
1/(Modulation index
h
). Format 8.8
Thus, 0x0200 represents the inverse
of a modulation index of 0.5. (MSK
or GMSK modulation imply h =
0.5). Valid range for
1/h
: 0.125 – 4
REG51: LSB
REG52: MSB
Modulation type
0 = 2-FSK
1 = 2-GFSK
2 = 4-FSK
3 = 4-GMSK
4 = 8-FSK
5 = 8-GMSK
REG30(5:0)
Continuous vs
burst mode
0 = burst mode
1 = continuous mode
While in continuous mode, the
following configuration parameters
are ignored: packet size, window
start and stop times.
REG30(6)
Spectrum
inversion
Whenever the received spectrum has
been inverted during the frequency
up and down-conversions, this bit
should be set. In particular, spectrum
inversion occurs in most COM-300x
receiver modules.
0 = off, 1 = on
REG11(5)
Nominal Center
frequency (
f
c_rx
)
Expected center frequency of the
received signal. 32-bit signed integer
(2’s complement representation)
expressed as
f
c_rx
* 2
32
/
f
clk_rx
Maximum recommended range: ± 10
MHz.
REG53: LSB,
REG54,
REG55,
REG56: MSB
BCH decoder
bypass
‘0’ = BCH decoder enabled
‘1’ = BCH decoder bypassed
REG32(4)
Receive packet
size
N
plrx
Receive burst size expressed in
number of payload symbols N
plrx
.
Must be an integer of 8.
REG31: LSB
REG32(3:0): MSb
Reception
window
start time
Start time of the window during
which the demodulator is allowed to
start receiving a frame.
In us after the first frame preamble in
a received superframe.
REG33: LSB
REG34
REG35: MSB
Reception
window end time
End time of the window during
which the demodulator is allowed to
start receiving a frame. A frame
reception in progress can extend
beyond the end of this window.
In us after the first frame preamble in
a received superframe.
REG36: LSB
REG37
REG38: MSB
Input selection
0 = digital real 12-bit unsigned
samples, right connector, COM-
3504.
1 = digital complex 2*12-bit
unsigned samples, right connector,
COM-3504.
2 = digital complex 2*10 or 2*12-bit
unsigned samples, left connector.
Compatible with most COM-30xx
modules.
7 = internal loopback mode, from
modulator. (not functional if the
symbol rate is selected with one
symbol per processing clock).
REG39(2:0)