
XRT79L71
PRELIMINARY
563
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
Some 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” ON PAGE 421., the E3, ITU-T G.832 frame consists of 537 bytes. Of these bytes, 530 bytes are
payload bytes and the remaining 7 bytes are overhead bytes. 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”RECEIVE 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 processo 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.
In order to accomplish this, the Receive Overhead Data Output Interface block has numerous output pins.
Table 70 presents a list and a brief definition of each of these pins.
FIGURE 258. 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.832 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)
Rx TTM
Controller
Block
Rx TTM
Controller
Block
Rx SSM
Controller
Block
Rx SSM
Controller
Block