Data Sheet

LJ1269HC
Rev1.0 Page 56 Web: www.ljelect.com
By default, if the CRC check fails then the FIFO is automatically cleared and no interrupt is generated. This filtering function can
be disabled via CrcAutoClearOff bit and in this case, even if CRC fails, the FIFO is not cleared and only PayloadReady interrupt
goes high. Please note that in both cases, the two CRC checksum bytes are stripped off by the packet handler and only the
payload is made available in the FIFO.
The CRC is based on the CCITT polynomial as shown below. This implementation also detects errors due to leading and trailing
zeros.
Figure 35. CRC Implementation
5.5.8. DC-Free Data Mechanisms
The payload to be transmitted may contain long sequences of 1's and 0's, which introduces a DC bias in the transmitted signal.
The radio signal thus produced has a non uniform power distribution over the occupied channel bandwidth. It also introduces
data dependencies in the normal operation of the demodulator. Thus it is useful if the transmitted data is random and DC free.
For such purposes, two techniques are made available in the packet handler: Manchester encoding and data whitening.
Note Only one of the two methods should be enabled at a time.
Manchester Encoding
Manchester encoding/decoding is enabled if DcFree = 01 and can only be used in Packet mode.
The NRZ data is converted to Manchester code by coding '1' as "10" and '0' as "01".
In this case, the maximum chip rate is the maximum bit rate given in the specifications section and the actual bit rate is half the
chip rate.
Manchester encoding and decoding is only applied to the payload and CRC checksum while preamble and Sync word are kept
NRZ. However, the chip rate from preamble to CRC is the same and defined by BitRate in RegBitRate (Chip Rate = Bit Rate
NRZ = 2 x Bit Rate Manchester).
Sub GHz FSK/OOK Transceiver Module DATASHEET