dp83251 National Semiconductor Corporation, dp83251 Datasheet - Page 9

• Manufacturer Part Number: dp83251
• Description: Player Device Fddi Physical Layer Controller
• Manufacturer: National Semiconductor Corporation

3 0 Functional Description
DATA REGISTERS
Data from the Configuration Switch is stored in the Data
Registers The 10-bit byte-wide data consists of a parity bit
a control bit and two 4-bit symbols as shown in Figure 3-3
PARITY CHECKER
The Parity Checker verifies that the parity bit in the Data
Register represents odd parity (i e odd number of 1s)
The parity checking is enabled and disabled through bit 6
(PRDPE) of the Current Transmit State Register (CTSR)
If a parity error occurs the Parity Checker will set bit 0 (DPE)
in the Interrupt Condition Register (ICR) and report the error
to the Repeat Filter
4B 5B ENCODER
The 4B 5B Encoder converts the two 4-bit symbols from
the Configuration Switch into their respective 5-bit codes
See Table 3-2 for the Symbol Encoding list
REPEAT FILTER
The Repeat Filter is used to prevent the propagation of
code violations in data frames to the downstream station
Upon receiving violations in data frames the Repeat Filter
replaces them with two Halt symbol pairs followed by Idle
symbols Thus the code violations are isolated and recov-
ered at each link and will not be propagated throughout the
entire ring
Details on Repeat Filter operation are described in Section
8 4
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) may not 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
More details on the operation of the Smoother can be found
in Section 8 5


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)
Parity Bit
b9
FIGURE 3-3 Byte-Wide Data
Control Bit
b8
b7
Data Bits
(Continued)
b0
9
LINE STATE GENERATOR
The Line State Generator allows the transmission of the
PHY Request data and can also generate and transmit Idle
Master Halt or Quiet symbol pairs which can be used to
implement the Connection Management procedures as
specified in the FDDI Station Management (SMT) docu-
ment
The Line State Generator is programmed through Transmit
bits 0 to 2 (TM
ter (CTSR)
Based on the setting of these bits the Transmitter Block
operates in the Transmit Modes where the Line State Gen-
erator overwrites the Repeat Filter and Smoother outputs
See Table 3-3 for the listing of the Transmit Modes
Active Transmit Mode
Off Transmit Mode
Idle Transmit Mode
Master Transmit Mode
Quiet Transmit Mode
Reserved Transmit
Mode
Halt Transmit Mode
JK
N
R
S
T
Symbol
TABLE 3-2 4B 5B Symbol Encoding
A
B
C
D
E
0
1
2
3
4
5
6
7
8
9
F
(Starting
Delimiter)
(Ending
Delimiter)
(Reset)
(Set)
k
TABLE 3-3 Transmit Modes
2 0
l
) of the Current Transmit State Regis-
Normal Transmission Mode
Transmit Quiet symbol pairs
and disable the Fiber Optic
Transmitter
Transmit Idle symbol pairs
Transmit Halt-Quiet symbol
pairs
Transmit Quiet symbol pairs
Reserved for future use If
selected Quiet symbol pairs
will be transmitted
Transmit Halt symbol pairs
4B Code
0100 or
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
0000
1101
0101
0110
0111
Outgoing 5B
11000 and
11110 or
11110
01001
10100
10101
01010
01011
01110
01111
10010
10011
10110
10111
11010
11011
11100
11101
11111
10001
01101
00111
11001