
76
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
HPR29) of a square wave of frequency
(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
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 119.44
μ
s
Example Access ID of 01110100 and control word 0100
HomePNA PHY Header
150.19
μ
s @ 1 Mbps
1 Tic = 116.6667 ns
= receiver blanking interval
HomePNA Header
Ethernet Packet
pulse
129 tics
potential
pulse position
22206B-41
Parameter
Value
Tolerance
Unit
CENTER_FREQUENCY
7.5
500 PPM
MHz
CYCLES_PER_PULSE
4
--
Cycles