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XRT79L71
PRELIMINARY
405
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
The Receive Overhead Data Output Interface block is the sixth functional block (within the Receive Direction)
of the XRT79L71 that we will discuss for E3, ITU-T G.751 Clear-Channel Framer Applications. Figure 184 presents an illustration of the "Receive Direction" circuitry, whenever the XRT79L71 has been configured to
operate in the E3, ITU-T G.751 Clear-Channel Framer Mode, with the Receive Overhead Data Output Interface
block highlighted.
Background Information
In order to fully understand the role of the Receive Overhead Data Output Interface, some background
information needs to be discussed first.
bits are payload bits and the remaining 12 bits are overhead bits. The XRT79L71 has been designed to handle
and process both the payload type and overhead type of bits/bytes for each E3 frame. Within the XRT79L71,
the Receive Payload Data Output Interface Block (which is discussed in considerable detail in SEE”THE payload data (that has been extracted from the incoming E3 data-stream) to the "System-Side" Terminal
Equipment. Likewise, the Receive Overhead Data Output Interface block has been designed to handle and
process the overhead bits.
The Receive Overhead Data Output Interface block unconditionally outputs the contents of all overhead bits
within the incoming E3 data-stream.
The XRT79L71 does not offer the user a means to shut off this
transmission of overhead data. However, the Receive Overhead Data Output Interface block does not provide
the user with the appropriate output signals for an external Data-Link Layer (or System-Side Terminal
Equipment) to sample and process these overhead bits.
FIGURE 184. 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 OVERHEAD DATA OUTPUT INTERFACE" 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)