LTC2272 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC2272' PDF : 44 Pages View PDF
LTC2273/LTC2272
APPLICATIONS INFORMATION
Frame Alignment Monitoring
After the initial synchronization has been established, it may
be desirable to periodically verify that frame alignment is
being maintained. The receiver may issue a synchroniza-
tion request at any time, but data will be lost during the
resynchronization interval.
To verify frame alignment without the loss of data, frame
alignment monitoring is enabled by setting the FAM pin
to a high level. In this mode, predetermined data in the
second code group of the frame is substituted with the
control character K28.7. The receiver is required to detect
the K28.7 character and replace it with the original data. In
this way, the second code group may be discerned from
the first, and the receiver is able to periodically verify the
frame alignment without the loss of data (refer to Table 1
and the flow diagram of Figure 18). There are two frame
alignment monitoring modes summarized in Table 1.
FAM mode 1 is implemented when FAM is high, and
SCRAM is low:
• When the data in the second code group of the current
frame equals the data in the second code group of the
previous frame, the LTC2273/LTC2272 will replace the
second code group with the control character K28.7
before serialization. However, if a K28.7 symbol was
already transmitted in the previous frame, the actual
code group will be transmitted.
• Upon receiving a K28.7 symbol, the receiver is required
to replace it with the data decoded at the same position
of the previous frame.
FAM mode 2 is implemented when FAM is high and
SCRAM is high:
• When the data in the second code group of the current
frame equals D28.7, the LTC2273/LTC2272 will replace
this data with K28.7 before serialization.
• Upon receiving a K28.7 symbol, the receiver is required
to replace it with D28.7.
With FAM enabled the receiver is required to search for
the presence of K28.7 symbols in the data stream. If two
successive K28.7 symbols are detected at the same posi-
tion other than the assumed end of frame, the receiver will
realign its frame boundary to the new position.
Table 1. Frame Alignment Monitoring Modes
SCRAM PIN
DDSYNC PIN
FAM Mode 1
Low
High
FAM Mode 2
High
High
FAM OFF
X
Low
ACTION
The second code group is replaced with K28.7 if
it is equal to the 2nd Code Group of the previous
frame
The second code group is replaced with K28.7 if
it is equal to D28.7
No K28.7 substitutions will take place
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