![](http://datasheet.mmic.net.cn/Exar-Corporation/XRT79L71IB-F_datasheet_100145/XRT79L71IB-F_275.png)
PRELIMINARY
XRT79L71
260
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
The user can accomplish this by setting Bit 6 (HDLC Controller Enable), within the Payload HDLC Control
Register to "0" as depicted below.
STEP 3 - Configure the XRT79L71 to operate in the E3, ITU-T G.751 Framing Format
The user can configure the XRT79L71 to operate in the E3, ITU-T G.751 Framing format by writing the
appropriate data into Bits 6 (IsDS3) and 2 (Frame Format) within the Framer Operating Mode Register
(Address = 0x1100), as depicted below.
The following table lists the relationship between the value of these bit-fields and the resulting framing formats
for the XRT79L71.
The XRT79L71 will be operating in the E3, ITU-T G.751 Framing Format, upon power-up or hardware reset.
NOTE: This bit setting configures the framing format for both the Transmit DS3/E3 Framer block and the Receive DS3/E3
Framer block.
Definition of the E3, ITU-T G.751 Overhead Bits
In general, the E3 ITU-T G.751 Overhead bits serve the following three purposes.
1.
To support Frame Synchronization between the Near-End and remote E3 Terminals.
2.
To (optionally) provide parity bits in order to facilitate performance monitoring and error detection within
the E3 data-stream.
Payload HDLC Control Register, (Address = 0x1182)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Framer
By-Pass
HDLC
Controller
Enable
HDLC
CRC-32
Unused
HDLC
Loop-back
Unused
R/W
R/O
R/W
R/O
0
Framer Operating Mode Register (Address = 0x1100)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Local
Loop back
IsDS3
Internal
LOS Enable
RESET
Direct
Mapped ATM
Frame
Format
TimReference Select [1:0]
R/W
0
1
0
1
0
1
TABLE 35: THE RELATIONSHIP BETWEEN THE CONTENTS OF BITS 2 (FRAME FORMAT) AND 6 (ISDS3) WITHIN THE
FRAMER OPERATING MODE REGISTER, AND THE RESULTING FRAMING FORMAT
BIT 6 (ISDS3)
BIT 2 (FRAME
FORMAT)
RESULTING FRAMING FORMAT OF XRT79L71
0
E3, ITU-T G.751
0
1
E3, ITU-T G.832
1
0
DS3, C-bit Parity
1
DS3, M13/M23