Silicon Laboratories SI4421 - Manual (Page 20)

Si4421
Bits 2-0 (f2 to f0): DQD threshold parameter.
The Data Quality Detector is a digital processing part of the radio, connected to the demodulator - it is an indicator
reporting the reception of an FSK modulated RF signal. It will work every time the receiver is on. Setting this
parameter defines how clean incoming data stream would be stated as good data (valid FSK signal).
If the internally calculated data quality value exceeds the DQD threshold parameter for five consecutive data bits
for both the high and low periods, then the DQD signal goes high.
The DQD parameter in the Data Filter Command should be chosen according to the following rules:
 The DQD parameter can be calculated with the following formula:
DQD
par
= 4 x (deviation – TX-RX
offset
) / bit rate
 It should be larger than 4 because otherwise noise might be treated as a valid FSK signal
 The maximum value is 7.
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 (f3 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: The synchron pattern consists of one or two bytes depending on the sp bit. Byte1 is fixed 2Dh, Byte0 can be programmed by
the Synchron Pattern Command (page 21).
Bit 2 (al): Set the input of the FIFO fill start condition:
al FIFO fill start condition
0 Synchron pattern
1 Always fill
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