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XRT79L71
PRELIMINARY
189
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
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 86 presents a simple illustration that depicts how the SFM
Synthesizer Block functions whenever it has been configured to operate in the Multiplexer Mode.
4.3.1.5.2.1
Configuring the SFM Synthesizer Block to operate in the Multiplexer Mode
The user can configure the SFM Synthesizer Block to operate in the Multiplexer Mode by executing 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
signal (via the E3CLK input pin) and it (2) will output ether one of these clock signals to the Clock and Data
Recovery block (depending upon whether the XRT79L71 has been configured to operate in the DS3 or E3
Mode).
FIGURE 86. 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
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)