![](http://datasheet.mmic.net.cn/Exar-Corporation/XRT79L71IB-F_datasheet_100145/XRT79L71IB-F_532.png)
XRT79L71
PRELIMINARY
517
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
value "0xF6" that is immediately followed by the FA2 byte which is of the value "0x28". In fact, the FA1 and
FA2 bytes are the very first two bytes to appear within each E3, ITU-T G.832 frame. The Receive E3 Framer
block will attempt to locate this 0xF628 pattern by performing five (5) different searches in parallel. The FA1
and FA2 Octet Search will be declared successful if the Receive E3 Framer block can locate a single
instantiation of the 0xF628 pattern. Once the Receive E3 Framer block detects this particular pattern, then it
will declare this instantiation of the 0xF628 pattern within the incoming E3 data-stream as a possible or
candidate FA1 and FA2 Octet within the incoming E3 data-stream. Additionally, the Receive E3 Framer block
will now transition to the FA1, FA2 Octet Verification State, within the E3 Frame Acquisition/Maintenance
The FA1, FA2 Octet Verification State
Once the Receive E3 Framer block has detected the 0xF628 pattern (e.g., the concatenation of the FA1 and
FA2 bytes), it must now verify that this pattern is indeed the FA1 and FA2 octets, and not some other set of
bytes within the incoming E3 data-stream that are mimicking the FA1 and FA2 bytes. Hence, the purpose of
the FA1, FA2 Octet Verification State is to implement this additional check on the Candidate FA1, FA2 Byte. In
order to clearly convey the mode that the Receive E3 Framer block is currently operating in, Figure 245 has
been repeated below, with the FA1 and FA2 Octet Verification state shaded.
FIGURE 246. THE STATE MACHINE DIAGRAM FOR THE RECEIVE E3 FRAMER BLOCK'S FRAME ACQUISITION/MAIN-
TENANCE
ALGORITHM (WITH THE FA1 AND FA2 OCTET SEARCH STATE SHADED)
FA1, FA2
Octet
Search
FA1, FA2
Octet
Search
LOF
State
LOF
State
OOF
State
OOF
State
In Frame
State
In Frame
State
FA1, FA2
Octet
Verification
FA1, FA2
Octet
Verification
FA1 and FA2 Octets
are detected Once
FA1 and FA2 Octets are
NOT Detected
FA1 and FA2 Octets
Are verified once
4 Consecutive
Invalid Frames
3 Consecutive
Valid Frames
1 or 3ms of operating
In the “OOF State”
(User Selectable)
Frame Maintenance
Mode