AM79C901AVCT datasheet(32/90 Pages) AMD

32 / 90 page

Am79C901A

PR ELI M IN AR Y

Figure 16.

HomePNA PHY Framing

HomePNA PHY Symbol Waveform

All HomePNA PHY symbols are composed at the transmit-

ter of a silence interval and a pulse formed of 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) that has been filtered with

an external bandpass filter. Data is encoded in the time in-

terval from the preceding pulse.

Table 6.

HomePNA PHY Pulse Parameters

Time Interval Unit

HomePNA PHY time intervals are expressed in Time

Interval 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 17.

An AID symbol is 129 TICs long. Transmit timing is

shown in Figure 17; receive timing in Figure 18. 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 sym-

bol 0) delineates the beginning of a HomePNA PHY

frame and is composed of a SYNC_START pulse, fol-

lowed by a SYNC_END pulse, after a fixed silence in-

terval as shown in Figure 17. 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 al-

lows for jitter by establishing a window around each

legal pulse position. This asymmetrical window is two

TICS wide on one side of the position and one TIC wide

on the other.

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

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

22304B-18

Note: Using default configurations.

Parameter

Value

Tolerance

Unit

CENTER_FREQUENCY

7.5

500 PPM

MHz

CYCLES_PER_PULSE

–

Cycles

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