Rainbow Electronics RF12B - Manual (Page 17)

RF12B
Bits 4 (s): Select the type of the data filter:
s Filter Type
0 Digital filter
1 Analog RC filter
Digital: This is a digital realization of an analog RC filter followed by a comparator with
hysteresis. The time constant is automatically adjusted to the bit rate defined by the Data Rate
Command .
Note: Bit rate can not exceed 115 kbps in this mode.
Analog RC filter: The demodulator output is fed to pin 7 over a 10 kOhm resistor. The filter
cut-off frequency is set by the external capacitor connected to this pin and VSS.
Bits 2-0 (f2 to f0): DQD threshold parameter.
Note: To let the DQD report "good signal quality" the threshold parameter should be 4 in cases where
the bit-rate is close to the deviation. At higher deviation/bit-rate settings, a higher threshold parameter
can report "good signal quality" as well.
The table shows the optimal filter capacitor values for different data rates
1.2 kbps 2.4 kbps 4.8 kbps 9.6 kbps 19.2 kbps 38.4 kbps 57.6 kbps 115.2 kbps 256 kbps
12 nF
8.2 nF 6.8 nF 3.3 nF 1.5 nF 680 pF 270 pF 150 pF 100 pF
Note: If analog RC filter is selected the internal clock recovery circuit and the FIFO can not be used.
7. FIFO and Reset Mode Command
bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 POR
1 1 0 0 1 0 1 0 f3 f2 f1 f0 sp al ff dr CA80h
Bits 7-4 (f4 to f0): FIFO IT level. The FIFO generates IT when the number of received data bits reaches
this level.
Bit 3 (sp): Select the length of the synchron pattern:
sp Byte1 Byte0 (POR) Synchron Pattern (Byte1+Byte0)
0 2Dh D4h 2DD4h
1 Not used D4h D4h
Note : Byte0 can be programmed by the Synchron Pattern Command.
Bit 2 (al): Set the input of the FIFO fill start condition:
al
0 Synchron pattern
1 Always fill
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