Rf12 – Rainbow Electronics RF12 User Manual

Page 16

RF12

4. Data Rate Command

bit 15 14 13 12 11 10 9

7 6 5 4 3 2 1 0 POR

1 1 0 0 0 1 1

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 maximal 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 be careful to use the

same division ratio in the receiver and in the transmitter.

5. Receiver Control Command

bit

14 13 12 11

10 9 8 7 6 5 4 3 2 1 0 POR

1 0 0 1 0 p20 d1

9080h

Bit 10 (p20): pin20 function select

p20 Function of pin 20

Interrupt input

VDI output

Bits 9-8 (d1 to d0): VDI (valid data indicator) signal response time setting:

Response

Fast

Medium

Slow

Always on

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