Silicon Laboratories SI4421 - Manual (Page 17)

Si4421
3. Frequency Setting Command
Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 POR
1 0 1 0 f11 f10 f9 f8 f7 f6 f5 f4 f3 f2 f1 f0 A680h
The 12-bit parameter F (bits f11 to f0) should be in the range
of 96 and 3903. When F value sent is out of range, the
previous value is kept. The synthesizer center frequency f
0
can be calculated as:
f
0
= 10 · C1 · (C2 + F/4000) [MHz]
The constants C1 and C2 are determined by
the selected band as:
Band [MHz] C1 C2
433 1 43
868 2 43
915 3 30
Band Minimum Frequency Maximum Frequency PLL Frequency Step
433 MHz 430.2400 MHz 439.7575 MHz 2.5 kHz
868 MHz 860.4800 MHz 879.5150 MHZ 5.0 kHz
915 MHz 900.7200 MHz 929.2725 MHz 7.5 kHz
4. Data Rate Command
Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 POR
1 1 0 0 0 1 1 0 cs r6 r5 r4 r3 r2 r1 r0 C623h
The actual bit rate in transmit mode and the expected bit rate of the received data stream in receive mode is determined by the 7-bit
parameter R (bits r6 to r0) and bit cs.
BR = 10000 / 29 / (R+1) / (1+cs · 7) [kbps]
In the receiver set R according to the next function:
R= (10000 / 29 / (1+cs · 7) / BR) – 1, where BR is the expected bit rate in kbps.
Apart from setting custom values, the standard bit rates from 600 bps to 115.2 kbps can be approximated with small error.
Data rate accuracy requirements:
Clock recovery in slow mode:  BR/BR < 1/(29 · N
bit
) Clock recovery in fast mode:  BR/BR < 3/(29 · N
bit
)
BR is the bit rate set in the receiver and  BR is the bit rate difference between the transmitter and the receiver. N
bit
is the maximum
number of consecutive ones or zeros in the data stream. It is recommended for long data packets to include enough 1/0 and 0/1
transitions, and to be careful to use the same division ratio in the receiver and in the transmitter.
5. Receiver Control Command
Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 POR
1 0 0 1 0 p16 d1 d0 i2 i1 i0 g1 g0 r2 r1 r0 9080h
Bit 10 (p16): Pin 16 function select
p16 Function of pin 16
0 Interrupt input
1 VDI output
17