AM79C978A AMD [Advanced Micro Devices], AM79C978A Datasheet - Page 75

• Manufacturer Part Number: AM79C978A
• Description: Single-Chip 1/10 Mbps PCI Home Networking Controller
• Manufacturer: AMD [Advanced Micro Devices]

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.
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.
CENTER_FREQUENCY
CYCLES_PER_PULSE
Fixed
14.93 s
SYNC
Symbol 0
Table 13. HomePNA PHY Pulse Parameters
129 tics
interval
SYNC
60 tics
Parameter
ACCESS ID interval
Fixed 120.39 s
AID
blanking
interval
ACCESS
ID Symbol
1
129 tics
01
20 tics
AID
blanking
interval
ACCESS
ID Symbol
2
129 tics
Value
Example Access ID of 01110100 and control word 0100
7.5
4
Access ID
HomePNA Header
11
AID
blanking
interval
ACCESS
ID Symbol
3
Tolerance
129 tics
500 PPM
Figure 38. HomePNA PHY Framing
66 tics
HomePNA PHY Header
–
151.14 s @ 1 Mbps
10
AID
blanking
interval
ACCESS
ID Symbol
4
pulse
129 tics
00
Cycles
Unit
MHz
Am79C978A
AID
blanking
interval
ACCESS
ID Symbol
5
Silence
129 tics
01
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.
PCOM
AID
blanking
interval
ACCESS
ID Symbol
6
1 Tic = 116.6667 ns
129 tics
4
00
= receiver blanking interval
Destination
potential
pulse position
Silence
interval
ACCESS
ID Symbol
7
6
129 tics
Source
6
Length
30.75 s
@ 1 Mbps
symbols
2
32 bits
PCOM
Ethernet Packet
Data
ETHERNET MAC and DATA
max 1500
Ethernet Packet
22304A-18
CRC
4
75