SM1212E433 Semtech, SM1212E433 Datasheet - Page 53

• Manufacturer Part Number: SM1212E433
• Description: RF Module For SX1212
• Manufacturer: Semtech
• Series: -r
• Type: Transceiver, ISMr

Specifications of SM1212E433

• Frequency: 433MHz
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• For Use With/related Products: SX1212E

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.
The CRC check is enabled by setting bit PKTParam_CRC_on. It is used for checking the integrity of the message.
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.
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.
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.
Rev 2 – June 18th, 2009
ADVANCED COMMUNICATIONS & SENSING
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.
data input
5.5.6. DC-Free Data Mechanisms
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5.5.5.4. CRC Based
5.5.6.1. Manchester Encoding
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Figure 45: CRC Implementation
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CRC Polynomial =X
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SX1212
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