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XRT7250 Datasheet, PDF (431/463 Pages) Exar Corporation – DS3/E3 FRAMER IC | |||
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XRT7250
DS3/E3 FRAMER IC
REV. 1.1.1
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FIGURE 202. FLOW CHART DEPICTING THE FUNCTIONALITY OF THE LAPD RECEIVER (CONTINUED)
From Figure 184
Generate the âReceive LAPD Message frameâ interrupt.
Compute âFrame Check Sequence (FCS)â value of incoming
LAPD Message Frame.
Compare âlocally-computedâ FCS value with that contained
within the newly received LAPD Message frames.
A
End
Do the
two FCS values
Yes
Match?
No
FCS Error Detected
Assert the âRx FCS Errorâ bit-field within the âRx E3
LAPD Status Register (Address = 0x19).
6.3.4 The Receive Overhead Data Output Inter-
face
Figure 203 presents a simple illustration of the Re-
ceive Overhead Data Output Interface block within
the XRT7250.
FIGURE 203. A SIMPLE ILLUSTRATION OF THE RECEIVE OVERHEAD OUTPUT INTERFACE BLOCK
RxOHFrame
RxOH
RxOHClk
RxOHEnable
RReecceeiviveeOOvveerrhheeaadd
OOuutptpuuttIInnteterrfafaccee
BBlolocckk
From Receive
E3 Framer Block
The E3, ITU-T G.832 frame consists of 537 bytes. Of
these bytes, 530 bytes are payload bits and the re-
maining 7 bytes are overhead bytes. The XRT7250
has been designed to handle and process both the
payload type and overhead type bytes for each E3
frame.
412
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