AM79C978 Advanced Micro Devices, AM79C978 Datasheet - Page 76

• Manufacturer Part Number: AM79C978
• Description: Single-Chip 1/10 Mbps PCI Home Networking Controller
• Manufacturer: Advanced Micro Devices

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 R 2 9 ) o f a s q u a r e w a v e o f f r e q u e n c y
(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.
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.
76
CENTER_FREQUENCY
CYCLES_PER_PULSE
Fixed
14.93 s
SYNC
Symbol 0
129 tics
interval
Table 11. HomePNA PHY Pulse Parameters
SYNC
60 tics
ACCESS ID interval
Fixed 119.44 s
Parameter
AID
blanking
interval
ACCESS
ID Symbol
1
129 tics
01
20 tics
AID
blanking
interval
ACCESS
ID Symbol
2
129 tics
Example Access ID of 01110100 and control word 0100
Access ID
HomePNA Header
Value
11
7.5
4
AID
blanking
interval
ACCESS
ID Symbol
3
129 tics
Tolerance
66 tics
500 PPM
HomePNA PHY Header
150.19 s @ 1 Mbps
10
Figure 37. HomePNA PHY Framing
--
AID
blanking
interval
ACCESS
ID Symbol
4
pulse
129 tics
00
Cycles
MHz
Unit
AID
blanking
interval
ACCESS
ID Symbol
5
Silence
129 tics
Am79C978
01
4 bytes
PCOM
AID
blanking
interval
ACCESS
ID Symbol
6
1 Tic = 116.6667 ns
129 tics
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.
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
PCOM
32 bits
Ethernet Packet
Data
ETHERNET MAC and DATA
max 1500
Ethernet Packet
CRC
4
22206B-41