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XRT79L71
PRELIMINARY
393
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
The Receive LAPD Controller block consists of the following sections.
The Receive LAPD Message Buffer
The Receive LAPD Controller
The Receive LAPD Message Buffer
The purpose of the Receive LAPD Message Buffer is to store the contents of LAPD/PMDL Messages that have
been received by the Receive LAPD Controller block. The Receive LAPD Message Buffer will serve as a
temporary storage location (of these incoming LAPD/PMDL Messages) until they can be read out by the
Microprocessor. The Receive LAPD Message Buffer is actually a 90 byte FIFO that is located at Indirect
Address Location 0x11C0 within the XRT79L71 address space.
The Receive LAPD Controller
The Receive LAPD Controller permits the user to receive path maintenance data link (PMDL) message from
the remote terminal equipment via the "inbound" E3 frames. In this case, the PMDL Message is extracted out
of the "N" bit-fields within each incoming E3 frame.
The on-chip Receive LAPD Controller is capable of
receiving 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 "Receive LAPD Message" buffer), to store the contents
of newly received PMDL Messages. The message format complies with ITU-T Q.921 (LAPD) protocol with
different addresses and is presented below in Figure 180.
FIGURE 179. ILLUSTRATION OF THE FUNCTIONAL BLOCK DIAGRAM OF THE RECEIVE DIRECTION CIRCUITRY, WHEN-
EVER THE
XRT79L71 HAS BEEN CONFIGURED TO OPERATE IN THE E3, ITU-T G.751 CLEAR-CHANNEL FRAMER
MODE (WITH THE "RECEIVE LAPD CONTROLLER" BLOCK HIGHLIGHTED)
Receive
Payload Data
Input
Interface
Block
Receive
Payload Data
Input
Interface
Block
Receive
DS3/E3
Framer
Block
Receive
DS3/E3
Framer
Block
Receive
DS3/E3
LIU Block
Receive
DS3/E3
LIU Block
RxSer
RxNib[3:0]
RxClk
RRING
RTIP
Receive
Overhead Data
Input Interface
Block
Receive
Overhead Data
Input Interface
Block
RxOHClk
RxOHInd
RxOH
RxOHEnable
RxOHFrame
RxNibClk
RxFrame
Rx LAPD
Controller
Block
Rx LAPD
Controller
Block
From Microprocessor
Interface Block
Rx LAPD
Buffer
(90 Bytes)
Rx LAPD
Buffer
(90 Bytes)