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S/UNI-QUAD
PMC-Sierra, Inc.
PM5349 S/UNI-QUAD
DATASHEET
PMC-971239 ISSUE 6 SATURN USER NETWORK INTERFACE (155-QUAD)
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
207
Figure 13: Conceptual Clocking Structure
Clock Synthesizer
Clock Recovery
Internal
Tx Clock
Source
A
B
RXD+/-
REFCLK
Internal
Rx Clock
Source
TCLK
Conceptual Clocking Structure
÷8
÷8
RCLK
Mode B
Internally
Loop timed
Mode A
Source timed
Mode A is provided for all public user network interfaces (UNIs) and for private
UNIs and private network node interfaces (NNIs) that are not synchronized to the
recovered clock.
The transmit clock in a private UNI or a private NNI may be locked to an external
reference or may free-run. The simplest implementation requires an oscillator
free-running at 19.44 MHz.
Mode A is selected by clearing the LOOPT bit of the Channel Control register.
REFCLK is multiplied by 8 to become the 155.52 MHz MHz transmit clock.
REFCLK must be jitter free. The source REFCLK is also internally used as the
clock recovery reference.
Mode B is provided for private UNIs and private NNIs that require synchronization
to the recovered clock. Mode B is selected by setting the LOOPT bit of the Master
Control register. Normally, the transmit clock is locked to the receive data. In the
event of a loss of signal condition, the transmit clock is synthesized from
REFCLK.