DP83255AVF datasheet(10/96 Pages) NSC

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30 Functional Description (Continued)

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 (ICk10l) of the Current Transmit State Register

(CTSR) to one of the following Injection Modes (see

Figure

3-4 )

1 No Injection (ie normal operation)

2 One Shot

3 Periodic

4 Continuous

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 e 0

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 (TBCg) and clocked out by the

Transmit Bit Clock (TXCg)

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

One Shot (Notes 1 3)

TLF10386 – 5

Periodic (Notes 2 3)

TLF10386 – 6

Continuous (Note 3)

TLF10386 – 33

Where

ISRA Injection Symbol Register A

ISRB Injection Symbol Register B

IJTR Injection Threshold Register

Note 1

In one shot when n a 0 the JK is replaced

Note 2

In periodic when n e 0 all symbols are replaced

Note 3

Max value on n e 255

FIGURE 3-4 Injection Modes

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