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PRELIMINARY
XRT79L71
56
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
STEP 2 - Configure the XRT79L71 to operate in the Clear-Channel Framer Mode
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 DS3 Mode
The user can choose between these two DS3 framing formats, by writing the appropriate data into Bits 2
(Frame Format) and 6 (IsDS3) 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 format
for the XRT79L71.
The XRT79L71 will be operating in the E3, ITU-T G.751 Framing format upon power-up or hardware reset.
Therefore, the user must write a "1" into both Bits 2 and 6 within this particular register in order to configure the
XRT79L71 to operate in the DS3, M13/M23 Mode.
NOTE: These bit setting configures the framing format for both the Transmit DS3/E3 Framer block and the Receive DS3/E3
Framer block.
Each of the two DS3 Frame Formats, as presented in Figure 14 and Figure 15, constitute an M-frame or a full
DS3 frame. Each M-frame consists of 7 680-bit F-frames, sometimes referred to as sub-frames. In Figure 14 and Figure 15 each F-frame is represented by the individual rows of payload and overhead bits. Each F-frame
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 For-
mat
TimRefSel[1:0]
R/W
0
1
0
1
0
1
TABLE 11: 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 (IS DS3)
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