AM79C978AVCW datasheet(75/256 Pages) AMD

75 / 256 page

Am79C978A

Figure 38.

HomePNA PHY Framing

HomePNA Symbol Waveform

At the transmitter, all HomePNA symbols are composed

of a silence interval and a pulse formed by an integer

number of cycles (TX_PULSE_CYCLES_P/N in HPR29)

of a square wave of frequency (CENTER_FREQUENCY

TX_PULSE_WIDTH in HPR29), which has been filtered

with a bandpass filter. Data is encoded in the time interval

from the preceding pulse. See Table 13.

Table 13.

HomePNA PHY Pulse Parameters

Time Interval Unit

HomePNA PHY time intervals are expressed in Time In-

terval Clock (TIC) units. One TIC is defined as 7/60E6

seconds or approximately 116.7 ns.

ACCESS ID Intervals

A HomePNA frame begins with an Access ID (AID) in-

terval which is composed of eight equally spaced sub-

intervals termed AID symbols 0 through 7 as shown in

Figure 38.

An AID symbol is 129 TICs long. Transmit timing is shown

in Figure 39; receive timing in Figure 40. Timing starts at

the beginning of each AID symbol at TIC = 0 and ends at

TIC = 129.

These symbols are described in the following sections.

Symbol 0 (SYNC interval)

SYNC Transmit Timing

The SYNC interval (AID symbol 0) delineates the begin-

ning of a HomePNA frame and is composed of a

SYNC_START pulse, followed by a SYNC_END pulse,

after a fixed silence interval as shown in Figure 39. Timing

for this (AID symbol 0) starts (TIC = 0) at the beginning of

the SYNC_START pulse. The SYNC_END pulse starts at

TIC = 126.

At TIC = 129, this AID symbol 0 ends and the next AID

symbol begins, with the symbol timing reference reset

to TIC = 0. No information bits are coded in the SYNC

(AID symbol 0 interval).

SYNC Receive Timing

As soon as the SYNC_START pulse is detected the

receiver disables (blanks) further detection until time TIC

= 61, after which detection is re-enabled for the next

received pulse. The receiver allows for jitter by establish-

ing a window around each legal pulse position. This win-

dow is two TICS wide on either side of the position.

A SYNC_END pulse that arrives outside the window of

the legal TIC = 126 is considered a noise event which is

used in setting the adaptive squelch level, aborts the

packet, and sets the receiver in search of a new

SYNC_START pulse and SYNC interval. If it is a transmit-

ting station, the COLLISION event is asserted as de-

scribed in the Collisions section.

SYNC

interval

Access ID

Silence

PCOM

Source

Destination

Length

ETHERNET MAC and DATA

max 1500

CRC

32 bits

PCOM

Ethernet Packet

Fixed

14.93

µs

AID

blanking

interval

AID

blanking

interval

AID

blanking

interval

AID

blanking

interval

AID

blanking

interval

AID

blanking

interval

60 tics

129 tics

Data

symbols

20 tics

66 tics

Silence

interval

SYNC

Symbol 0

ACCESS

ID Symbol

ACCESS

ID Symbol

ACCESS

ID Symbol

ACCESS

ID Symbol

ACCESS

ID Symbol

ACCESS

ID Symbol

ACCESS

ID Symbol

30.75

µs

@ 1 Mbps

ACCESS ID interval

Example Access ID of 01110100 and control word 0100

Fixed 120.39

µs

HomePNA PHY Header

151.14

µs @ 1 Mbps

1 Tic = 116.6667 ns

HomePNA Header

Ethernet Packet

pulse

129 tics

= receiver blanking interval

potential

pulse position

22304A-18

Parameter

Value

Tolerance

Unit

CENTER_FREQUENCY

7.5

500 PPM

MHz

CYCLES_PER_PULSE

–

Cycles

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