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XRT81L27
SEVEN CHANNEL E1 LINE INTERFACE UNIT WITH CLOCK RECOVERY
REV. 1.1.0
19
priority. This priority allows fast switching of channels
using “external hardware”. However, if software con-
trol is to be used, the PDTx pin must be tied low as
there is an internal pull-up resistor.
2.0
THE TRANSMIT SECTION
The Transmit section of the XRT81L27 consists of the
following blocks:
THE TRANSMIT LOGIC BLOCK
The Encoder block
The MUX block
The Timing Control block
The TX Pulse Shaper block
The Line Driver block
2.1
THE TRANSMIT LOGIC BLOCK.
The purpose of the Transmit Logic Block is to accept
either Dual-Rail or Single-Rail TTL/CMOS level data
and timing information from the Terminal Equipment.
Figure 7 illustrates the typical interface for the trans-
mission of data between the Terminal Equipment and
the Transmit Section of the XRT81L27.
2.1.1
Dual-rail input mode
The manner that the LIU handles Dual-Rail data is
described below and illustrated in
Figure 8. The
XRT81L27samples the data on the TPOS and TNEG
input pins on the falling edge of TCLK. If the
XRT81L27 samples a “1” on the TPOS input pin, the
Transmit Section of the device ultimately generates a
positive polarity pulse via the TTIP and TRING output
pins. If the XRT81L27 samples a “1” on the TNEG in-
put pin, the Transmit Section of the device generates
a negative polarity pulse via the TTIP and TRING out-
put pins. HDB3 Encoding will already have been done
on this data.
2.1.2
Single-rail input mode
Used if data is to be transmitted from the Terminal
Equipment to the XRT81L27 in Single-Rail format (a
binary data stream) without having to convert it into a
Dual-Rail format. The Transmit Logic Block accepts
Single-Rail data via the TPOS input pin. The TClk sig-
FIGURE 7. THE INTERFACE FOR THE TRANSMISSION OF DATA FROM THE TRANSMITTING TERMINAL EQUIPMENT TO
THE
TRANSMIT SECTION OF THE XRT81L27
Digital
Terminal
Equipment
(DTE)
Digital
Terminal
Equipment
(DTE)
TxPOS
TxNEG
TxClk
Transmit
Logic
Block
Transmit
Logic
Block
FIGURE 8. DUAL RAIL DATA FROM THE TERMINAL
TCLK
TPOS
TNEG
Data
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