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参数资料
| 型号： | SM1212E433 |
| 厂商： | Semtech |
| 文件页数： | 53/77页 |
| 文件大小： | 0K |
| 描述： | RF EVAL FOR SX1212 433MHZ ISM |
| 标准包装： | 1 |
| 类型： | 收发器，ISM |
| 频率： | 433MHz |
| 适用于相关产品： | SX1212E |
| 已供物品： | 模块，天线，电源，软件 |
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SX1212
ADVANCED COMMUNICATIONS & SENSING
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 =X 16 + X 12 + X 5 + 1
X 15
X 14
X 13
X 12
X 11
***
X 5
X 4
***
X 0
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.
Rev 2 – June 18th, 2009
Page 53 of 77
www.semtech.com
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