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XRT79L71
PRELIMINARY
151
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
Local-Timing/Asynchronous
Local-Timing/TxFrameRef
Loop-Timing
Each of these "Timing Reference" Modes is discussed in some detail below.
4.2.5.7.1
Local-Timing/Asynchronous Mode
If the XRT79L71 is configured to operate in the "Local-Timing/Asynchronous Mode, then all of the following is
true.
The Transmit DS3 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 DS3 traffic to the remote terminal equipment.
DS3 Frame Generation (e.g., the instant whenever the Transmit DS3 Framer block begins to generate and
transmit a new DS3 frame) is asynchronous with respect to any externally supplied clock signal to the
XRT79L71.
Configuring the XRT79L71 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, then do the following.
apply a 44.736MHz clock signal to the TxInClk input pin (Ball C10).
Tie the TxFrameRef input pin (Ball A11) to GND.
NOTE: Configuring the XRT79L71 to operate in the "Local-Timing/Asynchronous" Mode, is synonymous with configuring
the Transmit Payload Data Input Interface block into "Mode 3" (for Serial-Mode Applications - see
Section 4.2.1.3)4.2.5.7.2
Local-Timing/TxFrameRef Mode
If the XRT79L71 is configured to operate in the "Local-Timing/TxFrameRef Mode, then all of the following is
true.
The Transmit DS3 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 DS3 traffic to the remote terminal equipment.
The Transmit DS3 Framer block will initiate the generation (and transmission) of a new DS3 frame, anytime
it detects a rising edge at the TxFrameRef input pin. In this case DS3 Frame Generation (e.g., the instant
whenever the Transmit DS3 Framer block begins to generate and transmit a new DS3 frame) will be
synchronized to the signal that is applied to the TxFrameRef input pin.
Configuring the XRT79L71 to operate in the Local-Timing/TxFrameRef Mode
The uXRT79L71 can be configured to operate in the "Local-Timing/TxFrameRef" Mode by setting Bits 1 and 0
(TimRefSel[1:0]) within the Framer Operating Mode Register to "[0, 1]" as depicted below.
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 For-
mat
TimRefSel[1:0]
R/W
0
1
0
1
0
1