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PRELIMINARY
XRT79L71
304
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
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.
The Transmit LAPD Message Buffer
The purpose of the Transmit LAPD Message Buffer is to permit the user to write and temporarily store the
contents of the very next outbound LAPD Message that is to be transmitted. The Transmit LAPD Message
Buffer is actually a 90 byte FIFO that is located at Address location 0x11B0 within the XRT79L71 address
space.
The Transmit LAPD Controller
The Transmit LAPD Controller permits the user to transmit path maintenance data link (PMDL) messages to
the remote terminal equipment via the outbound E3 Frames. In this case the message bits are inserted into
and carried by the "N" bit within each outbound E3 frame. The on-chip Transmit LAPD Controller permits the
user to transmit both standard and non-standard PMDL Messages of any length up to 82 bytes.
The
XRT79L71 allocates a block of 90 bytes of on-chip RAM (e.g., the Transmit LAPD Message buffer), to store the
contents of the outbound PMDL message to be transmitted. The message format complies with ITU-T Q.921
(LAPD) protocol with different addresses and is presented below in Figure 144.
FIGURE 143. 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
Tranmit
DS3/E3
LIU Block
Tranmit
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)