參數(shù)資料
型號(hào)： DM9801A
文件頁(yè)數(shù)： 42/60頁(yè)
文件大?。?/td> 605K
代理商： DM9801A
DM9801A
1M Home Phoneline Network Physical Layer Single Chip Transceiver
42
Final
Version: DM9801A-DS-F01
May 30, 2001
1 Mbps Home Phoneline Network PHY
The integrated DM9801A transceiver is a physical layer
device supporting home phoneline networking. It provides
all of the PHY layer functions required to support 1 Mbps
data transfers over existing residential phone wiring.
All data bits are encoded into the relative time position of a
pulse with respect to the previous one. The wave-form on
the wire consists of a 7.5 MHz carrier sinusoid enclosed
within an exponential (bell shaped) envelope. The waveform
is produced by generating four 7.5 MHz square wave cycles
and passing them through an external bandpass filter.
The Home Phoneline Network PHY frame consists of a
Home Phoneline Network header that replaces the normal
Ethernet 64-bit preamble and delimiter. The frame header is
prepended to a standard Ethernet packet starting with the
destination address and ending with the CRC. Only the
PHY layer and its parameters are modified from that of the
standard Ethernet implementation. The Home Phoneline
Network PHY layer is designed to operate with a standard
Ethernet MAC layer controller implementing all the
CSMA/CD protocol features.
The frame begins with a characteristic SYNC interval that
delineates the beginning of a Home Phoneline Network
frame followed by an Access ID (AID) which encodes 8 bits
of AID and 4 bits of control word. The AID is used to detect
collisions and is dynamically assigned, while the control
word carries speed and power information. The AID is
followed by a silence interval, then 32 bits of data reserved
for PHY layer communication. These bits are accessible via
internal registers and are for future use.
Data encoding consists of two symbol types: an AID symbol
and a data symbol. The AID symbol is always transmitted at
the same speed and encodes 2 bits that determine the
pulse position (one of four) relative to the
previous pulse. These bits are transmitted LSB first.
The access symbol interval is fixed.
The data symbol interval is variable. The arriving bit stream
is blocked into from 3-bit to 6-bit blocks according to a
proprietary (RLL25) algorithm. The bits in each block are
then used to encode a data symbol. Each symbol consists
of a Data Inter Symbol Blanking Interval (DISBI) and then a
pulse at one of 25 possible positions. The pulse position and
polarity within the interval is determined by the bits in the
data block. Immediately after the pulse a new symbol
interval begins. During the DISBI the receiver ignores all
incoming pulses to allow network reflections to die out.
Any station may be programmed to assume the role of a
PHY master and remotely command, via the control word,
the rest of the units on the network to change their transmit
speed or power level.
Many of the framing parameters are programmable in
the Home Phoneline Network PHY and will allow
modifications to transmission speed center frequency as
well as noise and reflection rejection algorithms.
Two default speeds are provided, low at 0.7 Mbps and
high at 1 Mbps.
Home Phoneline Network PHY Medium Interface
Framing
The Home Phoneline Network frame on the phone wire
network consists of a header generated in the PHY
prepended to an IEEE 802.3 Ethernet data packet received
from the MAC layer.
When transmitting on the wire pair, the DM9801A first
receives an Ethernet MAC frame from the MAC. The 8
octets of preamble and delimiter are stripped off and
replaced with the Home Phoneline Network PHY header,
then transmitted on the home network with the LSB of each
symbol being transmitted first. During a receive operation,
the reverse process is executed. When a Home Phoneline
Network PHY frame is received by the DM9801A, the
header is stripped off and replaced with the 4 octets of
preamble and delimiter of the IEEE 802.3 Ethernet MAC
frame specification and then passed on to the MAC layer.
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