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RFM22B-868-S1 参数 Datasheet PDF下载

RFM22B-868-S1图片预览
型号: RFM22B-868-S1
PDF下载: 下载PDF文件 查看货源
内容描述: ISM收发器模块 [ISM TRANSCEIVER MODULE]
分类和应用: ISM频段
文件页数/大小: 70 页 / 2627 K
品牌: HOPERF [ HOPERF ]
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RFM22B/23B  
6.5. 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 128 kbps. The implementation of Manchester encoding is shown in  
Figure 24. 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." Figure 23 demonstrates the portions of the  
packet which have Manchester encoding, data whitening, and CRC applied. CRC can be applied to only the data  
portion of the packet or to the data, packet length and header fields. Figure 24 provides an example of how the  
Manchester encoding is done and also the use of the Manchester invert (enmaniv) function.  
Manchester  
Whitening  
CRC  
CRC  
(Over data only)  
Header/  
Address  
PK  
Length  
Preamble  
Sync  
CRC  
Data  
Figure 23. Operation of Data Whitening, Manchester Encoding, and CRC  
Data before Manchester  
1
1
1
1
1
1
1
1
0
0
0
1
0
Preamble = 0xFF  
First 4bits of the synch. word = 0x2  
Data after Machester ( manppol = 1, enmaninv = 0)  
Data after Machester ( manppol = 1, enmaninv = 1)  
Data before Manchester  
0
0
0
0
0
0
0
0
0
0
0
1
0
Preamble = 0x00  
First 4bits of the synch. word = 0x2  
Data after Machester ( manppol = 0, enmaninv = 0)  
Data after Machester ( manppol = 0, enmaninv = 1)  
Figure 24. Manchester Coding Example  
6.6. Preamble Detector  
The RFM22B/23B has integrated automatic preamble detection. The preamble length is configurable from 1–256  
bytes using the prealen[7:0] field in "Register 33h. Header Control 2" and "Register 34h. Preamble Length", as  
described in “6.2. Packet Configuration”. The preamble detection threshold, preath[4:0] as set in "Register 35h.  
Preamble Detection Control 1", is in units of 4 bits. The preamble detector searches for a preamble pattern with a  
length of preath[4:0].  
If a false preamble detect occurs, the receiver will continuing searching for the preamble when no sync word is  
detected. Once preamble is detected (false or real) then the part will then start searching for sync. If no sync occurs  
then a timeout will occur and the device will initiate search for preamble again. The timeout period is defined as the  
sync word length plus four bits and will start after a non-preamble pattern is recognized after a valid preamble  
detection. The preamble detector output may be programmed onto one of the GPIO or read in the interrupt status  
registers.  
Tel: +86-755-82973805 Fax: +86-755-82973550 E-mail: sales@hoperf.com http://www.hoperf.com  
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