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PRELIMINARY
XRT79L71
518
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
When the Receive E3 Framer block enters this state, it will then quit performing the bit-by-bit search within the
incoming E3 data-stream for the FA1 and FA2 bytes. Instead, the Receive E3 Framer block will read in the two
octets that occur 537 bytes (e.g., one E3 frame period later) after the Candidate FA1 and FA2 bytes were first
detected. If these two bytes exhibit the 0xF628 pattern, then the Receive E3 Framer block will conclude that it
has TRULY found the Framing Alignment FA1 and FA2 bytes and will transition into the In-Frame state.
However, if these two bytes do not exhibit the 0xF628 pattern, then the Receive E3 Framer block will conclude
that it has been fooled by data within the incoming E3 data-stream mimicking the FA1 and FA2 bytes, and will
transition back into the FA1, FA2 Octet Search state.
The In-Frame State
Once the Receive E3 Framer block while operating in the FA1, FA2 Octet Verification State detects the 0xF628
pattern, in the correct location (e.g., exactly one E3 frame period, after the Candidate FA1 and FA2 bytes were
first detected), then it will conclude that it has correctly located the FA1 and FA2 bytes, and it will transition into
the In-Frame state. Once the Receive E3 Framer block enters the In-Frame state, it will cease performing
Frame Acquisition functions, and it will begin to perform Frame Maintenance functions. A detailed description
of the Receive E3 Framer block, operating in the In-Frame state can be found in SEE”THE FRAME- The OOF (Out of Frame) State
If the Receive E3 Framer block, while operating in the In-Frame state, receives four (4) consecutive incoming
E3 frames, in which the FA1 or FA2 bytes are erred, then the Receive E3 Framer block will transition into the
OOF State. 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 OOF State shaded.
FIGURE 247. THE STATE MACHINE DIAGRAM FOR THE RECEIVE E3 FRAMER BLOCK'S FRAME ACQUISITION/MAIN-
TENANCE
ALGORITHM (WITH THE FA1 AND FA2 OCTET VERIFICATION 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