PRELIMINARY
XRT79L71
516
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
The operation of the Receive E3 Framer block, while in the Frame Acquisition mode, is best understood by
reviewing the Receive E3 Framer block's Frame Acquisition/Maintenance Algorithm state machine diagram,
The Receive E3 Framer block will be performing Frame Acquisition operation while it is operating in the
following states per the E3, ITU-T G.832 Frame Acquisition/Maintenance algorithm State Machine diagram, as
depicted in Figure 248.
FA1, FA2 Octet Search
FA1, FA2 Octet Verification
OOF State
LOF State
Once the Receive E3 Framer block enters the In-Frame state (per Figure 248), then it will begin Frame
Maintenance operation. The Receive E3 Framer block's operation in each of the Frame Acquisition states is
presented below.
The FA1, FA2 Octet Search State
When the XRT79L71 is first powered up, or exits a Hardware RESET event, the Receive E3 Framer block will
be operating in the Frame Acquisition Mode. At this point, the very first thing that the Receive E3 Framer block
will do is to begin to look for valid E3 frames within the incoming E3 data-stream by first searching for the FA1
and FA2 octets. At this initial point the Receive E3 Framer block will be operating in the FA1 and FA2 Octet
Search state within the E3 Frame Acquisition/Maintenance Algorithm state machine diagram. 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 Search state shaded.
FIGURE 245. THE RECEIVE E3 FRAMER BLOCK'S FRAME ACQUISITION/MAINTENANCE ALGORITHM - E3, ITU-T
G.832 APPLICATIONS
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