Rf12b – Rainbow Electronics RF12B User Manual

Page 17

RF12B

Bits 4 (s): Select the type of the data filter:

Filter Type

Digital filter

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

7 6 5 4 3 2 1 0 POR

1 1 0 0 1 0 1

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:

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:

Synchron pattern

Always fill

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