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XRT79L71
PRELIMINARY
117
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
The Transmit LAPD Controller block consists of the following sections.
The Transmit LAPD Message Buffer
The TransmitLAPD Controller
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 LAPD Transmitter
The LAPD Transmitter permits the user to transmit path maintenance data link (PMDL) messages to the
remote terminal equipment via the outbound DS3 Frames. In this case the message bits are inserted into and
carried by the 3 DL bit fields of F-Frame #5 within each DS3 M-frame. The on-chip LAPD Transmitter 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 52.
FIGURE 51. ILLUSTRATION OF THE FUNCTIONAL BLOCK DIAGRAM OF THE TRANSMIT DIRECTION CIRCUITRY, WHEN-
EVER THE
XRT79L71 HAS BEEN CONFIGURED TO OPERATE IN THE DS3 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)
Tx FEAC
Processor
Block
Tx FEAC
Processor
Block