AM79C901AJCT AMD [Advanced Micro Devices], AM79C901AJCT Datasheet - Page 32

• Manufacturer Part Number: AM79C901AJCT
• Description: HomePHY Single-Chip 1/10 Mbps Home Networking PHY
• Manufacturer: AMD [Advanced Micro Devices]

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.
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.
32
CENTER_FREQUENCY
CYCLES_PER_PULSE
Note: Using default configurations.
Table 6. HomePNA PHY Pulse Parameters
Fixed
14.93 s
SYNC
Symbol 0
129 tics
interval
SYNC
Parameter
60 tics
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
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
66 tics
HomePNA PHY Header
151.14 s @ 1 Mbps
10
Tolerance
500 PPM
AID
blanking
interval
ACCESS
ID Symbol
4
Figure 16. HomePNA PHY Framing
–
pulse
129 tics
00
P R E L I M I N A R Y
AID
blanking
interval
ACCESS
ID Symbol
5
Silence
Cycles
129 tics
MHz
Unit
01
Am79C901A
PCOM
AID
blanking
interval
ACCESS
ID Symbol
6
1 Tic = 116.6667 ns
129 tics
4
00
= receiver blanking interval
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.
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
CRC
4
22304B-18