RFM42 Datasheet, PDF (32/110 Pages) –

RFM42/43
6.4. Data Whitening, Manchester Encoding, and CRC
Data whitening can be used to avoid extended sequences of 0s or 1s in the transmitted data stream to achieve a
more uniform spectrum. When enabled, the payload data bits are XORed with a pseudorandom sequence output
from the built-in PN9 generator. The generator is initialized at the beginning of the payload. The receiver recovers the
original data by repeating this operation. Manchester encoding can be used to ensure a dc-free transmission and good
synchronization properties. When Manchester encoding is used, the effective datarate is unchanged but the actual
datarate (preamble length, etc.) is doubled due to the nature of the encoding. The effective datarate when using
Manchester encoding is limited to 64 kbps. Data Whitening and Manchester encoding can be selected with "Register
70h. Modulation Mode Control 1". The CRC is configured via "Register 30h. Data Access Control".
6.5. TX Retransmission and Auto TX
The RFM42/43 is capable of automatically retransmitting the last packet in the FIFO if no additional packets were
loaded into the TX FIFO. Automatic Retransmission is achieved by entering the TX state with the txon bit set. This
feature is useful for Beacon transmission or when retransmission is required due to the absence of a valid
acknowledgement. Only packets that fit completely in the TX FIFO are valid for retransmit. When it is necessary to
transmit longer packets, the TX FIFO uses the circular read/write capability.
An Automatic Transmission is also available. When autotx = 1 the transceiver will enter automatically TX State
when the TX FIFO is almost full. When the TX FIFO is empty the transceiver will automatically return to the IDLE
State.
Add R/W Function/Description D7 D6 D5 D4 D3
D2
POR
D1
D0
Def.
08 R/W
Operating &Function
Control 2
Reserved
autotx Reserved Reserved ffclrtx 00h
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