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XRT79L71
PRELIMINARY
329
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
Once these two steps are executed, then the Receive DS3/E3 Framer block will be configured to compute and
verify the BIP-4 nibble values within each incoming E3 frame. Further, the Transmit DS3/E3 Framer block will
be configured to automatically set the "A" bit (within its outbound E3 frame) to "1", anytime the Receive DS3/E3
Framer block detects and flags BIP-4 errors.
5.2.4.5
Setting the Transmit E3 Framer Block Timing Reference
When designing a system, a decision must be made to configure the system to operate in either the Local-
Timing Mode (e.g., where the timing source for the Transmit [or outbound] Direction traffic is derived from a
"local" [or in-system] clock source) or in the Loop-Timing Mode (e.g., where the timing source for the Transmit
[or outbound] Direction traffic is derived from the "remote terminal equipment's" clock source. The XRT79L71
can be configured to support either of these applications.
The XRT79L71 supports the following three (3) different "Timing Reference" Modes.
Local-Timing/Asynchronous
Local-Timing/TxFrameRef
Loop-Timing
5.2.4.5.1
Local-Timing/Asynchronous Mode
If the XRT 79L71 is configured to operate in the Local-Timing/Asynchronous Mode, then the following are true.
The Transmit E3 Framer block will use the clock signal that is applied to the "TxInClk" input pin as its timing
source, for generating and transmitting the outbound E3 traffic to the remote terminal equipment.
E3 Frame Generation (e.g., the instant whenever the Transmit E3 Framer block begins to generate and
transmit a new E3 frame) is asynchronous with respect to any externally supplied clock signal to the XRT
79L71.
Configuring the XRT 79L71 to operate in the Local-Timing/Asynchronous Mode
The XRT79L71 can be configured to operate in the "Local-Timing/Asynchronous" Mode by setting Bits 1 and 0
(TimRefSel[1:0]) within the Framer Operating Mode Register to "[1, 1]" as depicted below.
Requirements Associated with the "Local-Timing/Asynchronous" Mode
If the XRT79L71 is configured to operate in the "Local-Timing/Asynchronous" Mode, do the following.
Transmit E3 Configuration Register - G.751 (Address = 0x1130)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
TxBIP-4
Enable
TxASrcSel[1:0]
TxNSrcSel[1:0]
TxAIS
Enable
TxLOS
Enable
TxFAS
SourceSel
R/W
1
0
Framer Operating Mode Register (Address = 0x1100)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Framer
Local
Loop Back
IsDS3
Internal
LOS
Enable
RESET
Direct
Map
ATM
Frame
Format
TimRefSel[1:0]
R/W
0
1
0
1
0
1