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| 型號： | SSCP485 |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | SSC P485 PL Transceiver IC |
| 中文描述： | 南南合作P485特等收發(fā)芯片 |
| 文件頁數(shù)： | 11/19頁 |
| 文件大?。?/td> | 109K |
| 代理商： | SSCP485 |
SSC P485 PL Transceiver IC
July 1998
11
Revision 5
24000828
ADVANCE INFORMATION
Spread Spectrum Carrier
TM
Technology
Spread Spectrum Carrier
point-to-point or carrier sense multiple access (CSMA) networks. Historically, spread spectrum communication
systems have been used for secure communications and/or to overcome narrow-band impairments in the
communications medium. Spread spectrum receivers generally require an initial period of time to synchronize
with the carrier, so they have not been appropriate for CSMA networks. Spread Spectrum Carrier Technology is
a method by which a series of short, self-synchronizing, frequency swept "chirps" act as a carrier. The chirps are
always of the same known pattern and detectable by all of the nodes on the network. The chirp ranges in
frequency from 100 to 400 kHz over a duration of 100 μs. The chirp is swept from approximately 200 kHz to
400 kHz and then from 100 kHz to 200 kHz. Figure 8 illustrates the SSC power line chirp.
TM
(SSC) Technology is a method of spread spectrum communications suitable for both
Figure 8. Spread Spectrum Carrier Chirp
Preamble Encoding
Two modulation schemes are used for symbol transmission by the physical layer. Amplitude Shift Keying (ASK)
is used in the preamble of the message packet. ASK modulation uses SUPERIOR and INFERIOR states to
encode symbols. A SUPERIOR state is represented by the presence of a chirp and an inferior state by the
absence of a chirp. Because the transmitter is quiet during inferior states, superior states transmitted by other
devices contending for the channel can be detected during the preamble of the packet. An example of ASK
modulation is shown in Figure 9. Note that in the preamble, the duration of a symbol is slightly longer than in the
body of the packet. A preamble symbol is 114 μs in length. Symbols in the sync sequence and the Packet Body
are 100 μs in length. Please note the “Chirp” is ALWAYS 100μs in length and is followed by 14 μs of quiet time
during the preamble.
Data Encoding
Phase Reversal Keying (PRK) utilizes two phases of the SUPERIOR state, SUPERIOR S1 and SUPERIOR S2,
which are 180° out of phase with one another, to modulate the encoded data. This modulation technique is more
robust than the ASK technique, because it allows the P485 to correlate and track each symbol rather than just
those encoded as SUPERIOR states. Figure 9 shows an example of PRK.
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