AM79C978VCSLASHW datasheet(76/261 Pages) AMD

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Am79C978

Figure 37.

HomePNA PHY Framing

HomePNA Symbol Waveform

All HomePNA symbols are composed at the transmitter

of a silence interval, and a pulse formed of an integer

number of cycles (TX_PULSE_CYCLES_P/N in

H P R29 )

squar e

wa ve

f r e que ncy

(CENTER_FREQUENCY TX_PULSE_WIDTH in

HPR29) that has been filtered with a bandpass filter.

Data is encoded in the time interval from the preceding

pulse.

Table 11.

HomePNA PHY Pulse Parameters

Time Interval Unit

HomePNA PHY time intervals are expressed in Time

Interval Clock (TIC) units. One TIC is defined as

1/60E6 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 37.

An AID symbol is 129 TICs long. Transmit timing is

shown in Figure 38; receive timing in Figure 39. 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 be-

ginning 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 38.

Timing for this (AID symbol 0) starts (TIC = 0) at the be-

ginning 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 re-

ceiver 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 es-

tablishing a window around each legal pulse position.

This window is -2 +1 TICS wide on either side of the po-

sition.

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 trans-

mitting station, the COLLISION event is asserted as

described in the Collisions section.

SYNC

interval

Access ID

Silence

PCOM

4 bytes

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 119.44

µs

HomePNA PHY Header

150.19

µs @ 1 Mbps

1 Tic = 116.6667 ns

HomePNA Header

Ethernet Packet

pulse

129 tics

= receiver blanking interval

potential

pulse position

22206B-41

Parameter

Value

Tolerance

Unit

CENTER_FREQUENCY

7.5

500 PPM

MHz

CYCLES_PER_PULSE

Cycles

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