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PRELIMINARY
XRT79L71
364
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
The "SFM Synthesizer" block will then multiplex and route the appropriate clock signal (e.g., the 44.736MHz or
the 34.368MHz) to the Clock and Data Recovery, depending upon whether the XRT79L71 has been configured
to operate in the DS3 or the E3 Mode.
This mode is referred to as the "Multiplexer" Mode, because the "SFM Synthesizer" block can accept up to
both a 44.736MHz and a 34.368MHz via their respective inputs, and it will only output one of these clock
signals (to the Clock and Data Recovery block) depending upon which mode (e.g., either DS3 or E3) that the
XRT79L71 has been configured to operate in. Figure 168 presents a simple illustration that depicts how the
"SFM Synthesizer" Block functions whenever it has been configured to operate in the "Multiplexer" Mode.
Configuring the SFM Synthesizer Block to operate in the "Multiplexer" Mode
Toconfigure the "SFM Synthesizer" Block to operate in the "Multiplexer" Mode execute the following steps.
STEP 1 - Apply a 44.736MHz clock signal (if available) to the "DS3CLK/SFMCLK" input pin (Ball P16), and
apply a 34.368MHz clock signal (if available) to the "E3CLK" input pin (Ball M16).
STEP 2 - Set Bit 5 (SFM Enable) within the "LIU Channel Control" Register to "0" as depicted below.
Using the 44.736MHz/34.368MHz Synthesized Clock signal (from the SFM Synthesizer Block) as an
External Clock Signal
As mentioned earlier, if the SFM Synthesizer block has been configured to operate in the "Multiplexer Mode",
then it will (1) accept a 44.736MHz clock signal (via the DS3CLK/SFMCLK input pin), and a 34.368MHz clock
FIGURE 168. A SIMPLE ILLUSTRATION THAT DEPICTS HOW THE "SFM SYTHESIZER" BLOCK FUNCTIONS WHENEVER
IT HAS BEEN CONFIGURED TO OPERATE IN THE
"MULTIPLEXER" MODE
LIU Channel Control Register (Address = 0x1306)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Unused
SFM
Clock Out
Enable
SFM
Enable
LIU
Remote
Loop-back
Mode
LIU
Local
Loop-back
Mode
Unused
R/O
R/W
R/O
0
1
0
SFM
Synthesizer
Block
SFM
Synthesizer
Block
44.736MHz
Or
34.368MHz
To Clock Recovery
PLL Block
DS3CLK/SFMCLK
(Ball P16)
34.368MHz
E3CLK
(Ball M16)