XRT72L50 Datasheet, PDF (294/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
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TxE3 FAS Error Mask Register - 1 (Address = 0x49)
BIT 7
RO
0
BIT 6
Not Used
RO
0
BIT 5
RO
0
BIT 4
R/W
X
BIT 3
BIT 2
BIT 1
TxFAS_Error_Mask_Lower[4:0]
R/W
R/W
R/W
X
X
X
BIT 0
R/W
X
Inserting Errors into the BIP-4 nibble, within each outbound E3 frame.
The user can insert errors into the BIP-4 nibble, within each outbound E3 frame, by writing the appropriate data
into the TxE3 BIP-4 Error Mask Register.
As the Transmit E3 Framer block formulates the outbound E3 frames, the contents of the BIP-4 bits are
automatically XORed with the contents of this register. 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 contain all
“0’s” (the default value).
NOTE: This register is only active if the XRT72L50 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
R/W
0
BIT 6
BIT 5
Not Used
R/W
R/W
0
0
BIT 4
R/W
0
BIT 3
R/W
0
BIT 2
BIT 1
TxBIP-4 Mask[3:0]
R/W
R/W
0
0
BIT 0
R/W
0
5.2.5 The Transmit E3 Line Interface Block
The XRT72L50 Framer IC is a digital device that takes E3 payload and overhead bit information from some
terminal equipment, processes this data and ultimately, multiplexes this information into a series of outbound
E3 frames. However, the XRT72L50 Framer IC lacks the current drive capability to be able to directly 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 reliably received by the far-end receiver. Figure 108 presents a circuit drawing depicting the
Framer IC interfacing to an LIU (XRT73L00 DS3/E3/STS-1 Transmit LIU).
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