GS2975A Datasheet, PDF (19/27 Pages) Gennum Corporation – HD-LINX® III Multi-Rate SDI Automatic Reclocker with Dual Differential Outputs

4.6 4:1 Input Mux
The 4:1 input mux allows the connection of four independent streams of video/data.
There are four differential inputs (DDI[3:0] and DDI[3:0]). The active channel can be
selected via the DDI_SEL[1:0] pins. Table 4-1 shows the input selected for a given state
at DDI_SEL[1:0].
Table 4-1: Bit Pattern for Input Select
DDI_SEL[1:0]
00
01
10
11
Selected Input
DDI0
DDI1
DDI2
DDI3
The DDI inputs are designed to be DC interfaced with the output of the GS2974 Cable
Equalizer. There are on-chip 50Ω termination resistors which come to a common point
at the DDI_VT pins. Connect a 10nF capacitor to this pin and connect the other end of
the capacitor to ground. This terminates the transmission line at the inputs for optimum
performance.
If only one input pair is used, connect the unused positive inputs to +3.3V and leave the
unused negative inputs floating. This helps to eliminate crosstalk from potential noise
that would couple to the unused input pair.
4.7 Automatic and Manual Data Rate Selection
The GS2975A can be configured to manually lock to a specific data rate or automatically
search for and lock to the incoming data rate. The AUTO/MAN pin selects automatic
data rate detection mode (Auto mode) when HIGH and manual data rate selection mode
(Manual mode) when LOW.
In Auto mode, the SS[2:0] bi-directional pins become outputs and the bit pattern
indicates the data rate that the PLL is locked to (or previously locked to). The “search
algorithm” cycles through the data rates and starts over if that data rate is not found (see
Figure 4-3).
270Mb/s
1.485(1.4835)Gb/s
2.970(2.697)Gb/s
Figure 4-3: Data Rate Search Pattern
GS2975A HD-LINX® III Multi-Rate SDI Automatic
Reclocker with Dual Differential Outputs
Data Sheet
41487 - 4
April 2009
19 of 27