RF64W datasheet(53/76 Pages) HOPE

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ADVANCED COMMUNICATIONS & SENSING

Page 53 of 76

RF64

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Please note that the received length byte, as part of the payload, is not stripped off the packet and is made

available in the FIFO.

To disable this function the user should set the value of the PKTParam_Payload_length to the value of the FIFO

size selected.

5.5.5.4. CRC Based

The CRC check is enabled by setting bit PKTParam_CRC_on. It is used for checking the integrity of the message.

 On Tx side a two byte CRC checksum is calculated on the payload part of the packet and appended to the end

of the message.

 On Rx side the checksum is calculated on the received payload and compared with the two checksum bytes

received. The result of the comparison is stored in the PKTParam_CRC_status bit and CRC_OK IRQ source.

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 PKTParam_CRC_autoclr bit and in this case, even if CRC fails, the FIFO is not

cleared and only Payload_ready 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 in Figure 45. This implementation also detects errors due to

leading and trailing zeros.

data input

CRC Polynomial =X16 + X12 + X5 + 1

X15

X14

X13

X12

X11

* * *

Figure 45: CRC Implementation

5.5.6. 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. Please note that only one of the two methods should be enabled at a time.

5.5.6.1. Manchester Encoding

Manchester encoding/decoding is enabled by setting bit PKTParam_Manchester_on 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.

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