DP83256VF-AP NSC [National Semiconductor], DP83256VF-AP Datasheet - Page 15

• Manufacturer Part Number: DP83256VF-AP
• Manufacturer: NSC [National Semiconductor]

3 0 Functional Description
The Repeat Filter complies with the FDDI standard by ob-
serving the following (see Figure 3-5 )
F IDLE
W
nn
N
X
V
I
ALSZILSZ
H
R
S
T
JK
I
V
E TPARITY
E ALSZILSZ Not in Active Line State nor in Idle Line
TABLE 3-3 Abbreviations used in the
Repeat Filter State Diagram
Force Idle true when not in Active
Transmit Mode
Represents the symbols R or S or T
Parity error
Data symbols (for C
interface)
Data portion of a control and data symbol
mixture
Any symbol (i e don’t care)
Violation symbols or symbols inserted by
the Receiver Block
Idle symbols or symbols inserted by the
Receiver Block
Active Line State or Idle Line State (i e
PHY Invalid)
State (i e PHY Valid)
Halt Symbol
Reset Symbol
Set Symbol
Frame ending delimiter
Frame start delimiter
Idle symbol (Preamble)
Code violations
e
0 in the PHY-MAC
(Continued)
15
Figure 3-6 describes the Smoother state diagram
1 In Repeat State violations cause transitions to Halt State
2 When Ix is encountered the Repeat Filter goes to the Idle
3 The Repeat Filter goes to the Repeat State following a JK
The END State which is not part of the FDDI PHY standard
allows an R or S prior to a T within a frame to be recognized
as a violation It also allows NT to end a frame as opposed
to being treated as a violation
SMOOTHER
The Smoother is used to keep the preamble length of a
frame to a minimum of 6 Idle symbol pairs
Idle symbols in the preamble of a frame may have been
added or deleted by each station to compensate for the
difference between the Receive Clock and its Local Clock
The preamble needs to be maintained at a minimum length
to allow stations enough time to complete processing of one
frame and prepare to receive another Without the Smooth-
er function the minimum preamble length (6 Idle symbol
pairs) cannot be maintained as several stations may con-
secutively delete Idle symbols
The Smoother attempts to keep the number of Idle symbol
pairs in the preamble at 7 by
and or
The Smoother Counter starts counting upon detecting an
Idle symbol pair It stops counting upon detecting a JK sym-
bol pair
and two Halt symbol pairs are transmitted (unless JK or Ix
occurs) followed by transition to Idle State
State during which Idle symbol pairs are transmitted until
a JK is encountered
from any state
Deleting an Idle symbol pair in preambles which have
more than 7 Idle symbol pairs
Inserting an idle symbol pair in preambles which have
less than 7 idle symbol pairs (i e Extend State)