Am79C978A
75
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
4
Source
6
6
Destination
Length
2
ETHERNET MAC and DATA
max 1500
CRC
4
32 bits
PCOM
Ethernet Packet
Fixed
14.93
μ
s
AID
blanking
interval
AID
blanking
interval
AID
blanking
interval
AID
blanking
interval
AID
blanking
interval
AID
blanking
interval
01
11
10
00
01
00
60 tics
129 tics
129 tics
129 tics
129 tics
129 tics
129 tics
129 tics
Data
symbols
20 tics
66 tics
Silence
interval
SYNC
Symbol 0
ACCESS
ID Symbol
1
ACCESS
ID Symbol
2
ACCESS
ID Symbol
3
ACCESS
ID Symbol
4
ACCESS
ID Symbol
5
ACCESS
ID Symbol
6
ACCESS
ID Symbol
7
30.75
μ
s
@ 1 Mbps
ACCESS ID interval
Fixed 120.39
μ
s
Example Access ID of 01110100 and control word 0100
HomePNA PHY Header
151.14
μ
s @ 1 Mbps
1 Tic = 116.6667 ns
= receiver blanking interval
HomePNA Header
Ethernet Packet
pulse
129 tics
potential
pulse position
22304A-18
Parameter
Value
Tolerance
Unit
CENTER_FREQUENCY
7.5
500 PPM
MHz
CYCLES_PER_PULSE
4
–
Cycles