GS2986 Datasheet, PDF (22/41 Pages) Gennum Corporation – Standards indication in Auto mode

Tx signal after de-emphasis
0.6
V1
0.4
0.2
V2
0
De-emphasis (dB)
=20 log (V1/V2)
-V2
-0.2
-0.4
-V1
-0.6 11110000 pattern
268
269
270
271
272
273
274
275
UI
Figure 4-2: De-emphasis Waveform
4.10 Automatic and Manual Data Rate Selection
The GS2986 can be configured to manually lock to a specific data rate or automatically search
for and lock to the incoming data rate. The default configuration is AUTO mode. This can be
changed via the host interface.
In AUTO mode, the SS[1:0] registers become read only, and the bit pattern indicates the data rate
at which the PLL is currently 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).
A “search algorithm” cycles through the supported data rates until lock is achieved, as shown in
Figure 4-3 below.
Power up
270Mb/s
1485Mb/s
2970Mb/s
*Note: the search algorithm does not necessarily begin with 270Mb/s.
Figure 4-3: GS2986 Automatic Mode Search Algorithm
In MANUAL mode, the SS[1:0] registers become read or write pins become inputs and the data
rate can be programmed. In this mode, the search algorithm is disabled and the GS2986's PLL
GS2986 Multi-Rate SDI Reclocker with Equalization &
De-emphasis
Data Sheet
52134 - 3
July 2012
22 of 41