PMC-Sierra, Inc.
PRELIMINARY
PM5381 S/UNI-2488
DATASHEET
PMC-2000489
ISSUE 1
SATURN USER NETWORK INTERFACE FOR 2488 MBIT/S
12
OPERATION
12.1.1 LVDS Overview
The LVDS APS Port implements the 777.6 Mb/s LVDS links. A reference clock of 77.76MHz is
required (which is generated from the S/UNI-2488 CSU). Four 777.6 Mb/s LVDS form a high-
speed serial TeleCombus interface for passing an STS-48 aggregate data stream.
A generic LVDS link according to IEEE 1596.3-1996 is illustrated below. The transmitter drives a
differential signal through a pair of 50Ω characteristic interconnects, such as board traces,
backplane traces, or short lengths of cable. The receiver presents a 100Ω differential termination
impedance to terminate the lines. Included in the standard is sufficient common-mode range for
the receiver to accommodate as much as 925mV of common-mode ground difference.
Figure 17: Generic LVDS Link Block Diagram
Transmitter
Interconnect
Receiver
Zo=50Ω
V
op
on
V
ip
in
100Ω
V
V
Zo=50Ω
Complete SERDES transceiver functionality is provided. Ten-bit parallel data is sampled by the
line rate divided-by-10 clock (77.76MHz SYSCLK) and then serialized at the line rate on the
LVDS output pins by a 777.6MHz clock synthesized from a divided version of REFCLK. Serial
line rate LVDS data is sampled and de-serialized to 10-bit parallel data. Parallel output transfers
are synchronized to a gated line rate divided-by-10 clock. The 10-bit data is passed to an 8B/10B
decoding block. The gating duty cycle is adjusted such that the throughput of the parallel
interface equals the receive input data rate (Line Rate +/- 100ppm). It is expected that the clock
source of the transmitter is the same as the clock source of the receiver to ensure the data
throughput at both ends of the link are identical.
Data must contain sufficient transition density to allow reliable operation of the data recovery
units. 8B/10B block coding and decoding is provided by the T8TE and R8TD blocks.
Proprietary and Confidentail to PMC-Sierra Inc., and for its Customer’s Internal Use
430
PMC [ PMC-SIERRA, INC ]
