dp83251 National Semiconductor Corporation, dp83251 Datasheet - Page 10

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

3-4 )
3 0 Functional Description
INJECTION CONTROL LOGIC
The Injection Control Logic replaces the data stream with a
programmable symbol pair This function is used to transmit
data other than the normal data frame or Line States
The Injection Symbols overwrite the Line State Generator
(Transmit Modes) and the Repeat Filter and Smoother out-
puts
These programmable symbol pairs are stored in the Injec-
tion Symbol Register A (ISRA) and Injection Symbol Regis-
ter B (ISRB) The Injection Threshold Register (IJTR) deter-
mines where the Injection Symbol pair will replace the data
symbols
The Injection Control Logic is programmed through the bits
0 and 1 (IC
(CTSR) to one of the following Injection Modes (see Figure
1 No Injection (i e normal operation)
2 One Shot
3 Periodic
4 Continuous
k
1 0
l
) of the Current Transmit State Register
One Shot (Notes 1 3)
Periodic (Notes 2 3)
Continuous (Note 3)
Where
Note 1 In one shot when n
Note 2 In periodic when n
Note 3 Max value on n
ISRA Injection Symbol Register A
ISRB Injection Symbol Register B
IJTR Injection Threshold Register
(Continued)
FIGURE 3-4 Injection Modes
e
255
e
a
0 all symbols are replaced
0 the JK is replaced
10
In the No Injection mode the data stream is transmitted
unchanged
In the One Shot mode ISRA and ISRB are injected once on
the nth byte after a JK where n is the programmed value
specified in the Injection Threshold Register
In the Periodic mode ISRA and ISRB are injected every nth
symbol
In the Continuous mode all data symbols are replaced with
the contents of ISRA and ISRB This is the same as periodic
mode with IJTR
SHIFT REGISTER
The Shift Regiser converts encoded parallel data to serial
data The parallel data is clocked into the Shift Register by
the Transmit Byte Clock (TBC
Transmit Bit Clock (TXC
NRZ TO NRZI ENCODER
The NRZ to NRZI Encoder converts the serial Non-Return-
To-Zero data to Non-Return-To-Zero-Invert-On-One data
This function can be enabled and disabled through bit 6
(TNRZ) of the Mode Register (MR) When programmed to
‘‘0’’ it converts the bit stream from NRZ to NRZI When
programmed to ‘‘1’’ the bit stream is transmitted NRZ
e
0
TL F 10386 – 33
g
)
TL F 10386 – 5
g
) and clocked out by the
TL F 10386 – 6