![](http://datasheet.mmic.net.cn/Exar-Corporation/XRT79L71IB-F_datasheet_100145/XRT79L71IB-F_486.png)
XRT79L71
PRELIMINARY
471
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
TASK # 3a - The System-Side Terminal Equipment must assert the TxOHIns input pin by setting it "High".
TASK # 3b - The System-Side Terminal Equipment must set the TxOH input pin to "1".
After the System-Side Terminal Equipment has executed these two sub-tasks, it must now move on to TASK #
4.
TASK # 4 - The System-Side Terminal Equipment must continue to sample the TxOHEnable output pin from
the XRT79L71. Whenever the System-Side Terminal Equipment samples the TxOHEnable low then it must
negate the TxOHIns input pin (e.g., by setting it to "0"). Afterwards, the System-Side Terminal Equipment
should then reset the internal TxOHEnable counter to "0", and return to TASK # 1.
6.2.3
TRANSMIT LAPD CONTROLLER BLOCK
The Transmit LAPD Controller block is the third functional block within the Transmit Direction of the XRT79L71
that we will discuss for E3, ITU-T G.832 Clear-Channel Framer Applications.
illustration of the Transmit Direction circuitry whenever the XRT79L71 has been configured to operate in the
E3, ITU-T G.832 Clear-Channel Framer Mode, with the Transmit LAPD Controller block highlighted.
The Transmit LAPD Controller block consists of the following sections.
The Transmit LAPD Message Buffer
The Transmit LAPD Controller
Each of these sections is described in some detail below.
FIGURE 225. ILLUSTRATION OF THE FUNCTIONAL BLOCK DIAGRAM OF THE TRANSMIT DIRECTION CIRCUITRY, WHEN-
EVER THE
XRT79L71 HAS BEEN CONFIGURED TO OPERATE IN THE E3 , ITU-T G.751 CLEAR-CHANNEL FRAMER
MODE (WITH THE TRANSMIT LAPD CONTROLLER BLOCK HIGHLIGHTED)
Transmit
Payload Data
Input
Interface
Block
Transmit
Payload Data
Input
Interface
Block
Transmit
DS3/E3
Framer
Block
Transmit
DS3/E3
Framer
Block
Transmit
DS3/E3
LIU Block
Transmit
DS3/E3
LIU Block
TxSer
TxNib[3:0]
TxInClk
TRING
TTIP
Transmit
Overhead Data
Input Interface
Block
Transmit
Overhead Data
Input Interface
Block
TxOHClk
TxOHIns
TxOHInd
TxOH
TxOHEnable
TxOHFrame
TxNibClk
TxFrame
Tx LAPD
Controller
Block
Tx LAPD
Controller
Block
From Microprocessor
Interface Block
Tx LAPD
Buffer
(90 Bytes)
Tx LAPD
Buffer
(90 Bytes)
Tx TTM
Controller
Block
Tx TTM
Controller
Block
Tx SSM
Controller
Block
Tx SSM
Controller
Block