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XRT79L71
PRELIMINARY
237
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
If the Receive DS3/E3 Framer block is operating in the DS3, C-bit Parity Mode, then the FEAC bit-field within
the DS3 Frame can be used to receive FEAC (Far End Alarm and Control) messages (See Figure 101). Each
FEAC code word is actually six bits in length. However, this six bit FEAC Code word is encapsulated with 10
framing bits to form a 16 bit message of the form:
where D5, D4, D3, D2, D1, D0 is the FEAC Code word. The rightmost bit (e.g., a "1") will be received first.
Since each DS3 Frame contains only 1 FEAC bit-field, 16 DS3 Frames are required to transmit the 16 bit
FEAC code message. The six bits, labeled x can represent 64 distinct messages, of which 43 have been
defined in the standards.
The Receive FEAC Controller block frames and validates the incoming FEAC data from the remote Transmit
FEAC Controller block via the received FEAC channel. Additionally, the Receive FEAC Controller block will
write the Received FEAC code words into an 8 bit Receive DS3 FEAC register. Framing is performed by
looking for two "0s" spaced 6 bits apart preceded by 8 "1s". The Receive FEAC Controller block contains two
registers that support FEAC Message Reception.
Receive DS3 FEAC Register (Address = 0x1116)
FIGURE 100. ILLUSTRATION OF THE FUNCTIONAL BLOCK DIAGRAM OF THE RECEIVE DIRECTION CIRCUITRY, WHEN-
EVER THE
XRT79L71 HAS BEEN CONFIGURED TO OPERATE IN THE DS3 CLEAR-CHANNEL FRAMER MODE (WITH THE
RECEIVE FEAC CONTROLLER BLOCK HIGHLIGHTED)
FIGURE 101. THE BIT-FORMAT OF THE FEAC MESSAGE
FEAC CODE WORD
FRAMING
0
D5
D4
D3
D2
D1
D0
0
1
Receive
Payload Data
Output
Interface
Block
Receive
Payload Data
Output
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
Output Interface
Block
Receive
Overhead Data
Output 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 FEAC
Processor
Block
Rx FEAC
Processor
Block