![](http://datasheet.mmic.net.cn/Exar-Corporation/XRT79L71IB-F_datasheet_100145/XRT79L71IB-F_177.png)
PRELIMINARY
XRT79L71
162
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
within the Jitter Attenuator FIFO and overwriting data that the XRT79L71 has yet had an opportunity to read it
out. This phenomenon will cause the XRT79L71 to drop or lose data.
Please see
Section 4.2.6.2.4 for information on how the Jitter Attenuator block responds to a FIFO Overflow or
Underflow condition.
The next few sections describe how to configure and use the Jitter Attenuator block
4.2.6.2.2
Enabling the Jitter Attenuator Block and selecting the Jitter Attenuator FIFO Size
The user will both enable the Jitter Attenuator block and select (and implement) a FIFO size by writing the
appropriate values into Bits 0 (Jitter Attenuator PLL/FIFO Operation Mode - Bit 0) and 2 (Jitter Attenuator PLL/
FIFO Operation Mode - Bit 2), as depicted below.
Table 24 presents the relationship between the states of Bits 2 and 0 (within the Jitter Attenuator Control
Register) and the (1) Enable/Disable State of the Jitter Attenuator, and (2) the Size of the Jitter Attenuator
FIFO.
If the Jitter Attenuator is enabled, then it will perform its Jitter Attenuation processing on any DS3 or E3 signal
that passes through it. However, if the Jitter Attenuator is disabled, then the Narrow-band PLL (within the Jitter
Attenuator) will be by-passed. In this case, the Jitter Attenuator block will operate in a transparent mode (e.g.,
the DS3 or E3 signal will pass through the Jitter Attenuator block with no jitter attenuation processing
performed on it, at all).
4.2.6.2.3
Configuring the Jitter Attenuator to operate in the Transmit or Receive Path
The user can configure the Jitter Attenuator block to operate in either the Transmit or Receive Direction, by
writing the appropriate value into Bit 1 (Jitter Attenuator in Transmit Path), within the Jitter Attenuator Control
Register as depicted below.
Jitter Attenuator Control Register (Address = 0x1307)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Unused
DFL
Jitter
Attenuator
FIFO Pointer
RESET
Jitter
Attenuator
PLL/FIFO
Operating
Mode - Bit 1
Jitter
Attenuator
in
Transmit
Path
Jitter
Attenuator
PLL/FIFO
Operating
Mode - Bit 0
R/O
R/W
0
X
0
X
TABLE 24: THE RELATIONSHIP BETWEEN THE STATES OF BITS 2 AND 0 (WITHIN THE JITTER ATTENUATOR CONTROL
REGISTER) AND THE (1) ENABLE/DISABLE STATE OF THE JITTER ATTENUATOR, AND (2) THE SIZE OF THE JITTER
ATTENUATOR FIFO
BIT 2
BIT 0
JITTER ATTENUATOR STATE
FIFO SIZE
0
Enabled
16 bits
0
1
Disabled
N/A
1
0
Enabled
32 bits
1
Disabled
N/A