XRT7250 Datasheet, PDF (294/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

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XRT7250
DS3/E3 FRAMER IC
REV. 1.1.1
As the Transmit E3 Framer block formulates the out-
bound E3 frames, the contents of the BIP-4 bits are
automatically XORed with the contents of this regis-
ter. The results of this XOR operation is written back
into the corresponding bit-field within the outbound
E3 frame, and is transmitted to the Remote Terminal
Equipment. Therefore, if the user does not wish to
modify any of these bits, then this register must con-
tain all “0’s” (the default value).
NOTE: This register is only active if the XRT7250 Framer IC
has been configured to insert the BIP-4 nibble into each
outbound E3 frame.
TXE3 BIP-4 ERROR MASK REGISTER (ADDRESS = 0X4A)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Not Used
TxBIP-4 Mask[3:0]
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
0
0
0
0
0
0
0
5.2.5 The Transmit E3 Line Interface Block
The XRT7250 Framer IC is a digital device that takes
E3 payload and overhead bit information from some
terminal equipment, processes this data and ulti-
mately, multiplexes this information into a series of
outbound E3 frames. However, the XRT7250 Framer
IC lacks the current drive capability to be able to di-
rectly transmit this E3 data stream through some
transformer-coupled coax cable with enough signal
strength for it to be received by the remote receiver.
Therefore, in order to get around this problem, the
Framer IC requires the use of an LIU (Line Interface
Unit) IC. An LIU is a device that has sufficient drive
capability, along with the necessary pulse-shaping
circuitry to be able to transmit a signal through the
transmission medium in a manner that it can be reli-
ably received by the far-end receiver. Figure 120 pre-
sents a circuit drawing depicting the Framer IC inter-
facing to an LIU (XRT7300 DS3/E3/STS-1 Transmit
LIU).
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