PMC-Sierra PM5349 manual Conceptual Clocking Structure

PMC-Sierra, Inc.

S/UNI-QUAD

DATASHEET

PM5349 S/UNI-QUAD

PMC-971239 ISSUE 6 SATURN USER NETWORK INTERFACE (155-QUAD)

Figure 13: Conceptual Clocking Structure

Conceptual Clocking Structure

RE F CLK

Internal

Tx Clock

Source

Internal

Rx Clock

Source

A

B

Clock Synthesizer

÷8TCLK

M o d e A

Source tim ed

M o d e B

Internally Loop tim ed

RXD+/- Clock Recov ery ÷8 RC LK

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.

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