LTC2274 Linear Technology, LTC2274 Datasheet - Page 29

• Manufacturer Part Number: LTC2274
• Description: 105Msps Serial Output ADC
• Manufacturer: Linear Technology

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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 fi rst, and the receiver is able to periodically verify the
frame alignment without the loss of data (refer to Table 1
and the fl ow 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
Table 1. Frame Alignment Monitoring Modes
FAM Mode 1
FAM Mode 2
FAM OFF
SCRAM PIN
High
Low
X
DDSYNC PIN
High
High
Low
• Upon receiving a K28.7 symbol, the receiver is required
FAM mode 2 is implemented when FAM is high and
SCRAM is high:
• When the data in the second code group of the current
• Upon receiving a K28.7 symbol, the receiver is required
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.
previous frame, the LTC2274 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.
to replace it with the data decoded at the same position
of the previous frame.
frame equals D28.7, the LTC2274 will replace this data
with K28.7 before serialization.
to replace it with D28.7.
The second code group is replaced with K28.7 if
it is equal to the 2
frame
The second code group is replaced with K28.7 if
it is equal to D28.7
No K28.7 substitutions will take place
nd
Code Group of the previous
ACTION
LTC2274
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