GS2985 Datasheet, PDF (25/45 Pages) Gennum Corporation – Uses standard 27MHz crystal

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: GS2985 Automatic Mode Search Algorithm
In MANUAL mode, the SS[1:0] pins become inputs and the data rate can be programmed.
In this mode, the search algorithm is disabled and the GS2985's PLL will only lock to the
data rate selected in accordance with Table 4-8.
Table 4-8: Data Rate Indication/Selection Bit Pattern
SS[1:0]
0
1
2
3
Data Rate (Mb/s)
Reserved
270
1485 or 1485/1.001
2970 or 2970/1.001
4.11 SD/HD Indication
The SD/HD signal indicates the output data rate of the device and can be connected to
the SD/HD input pin of dual slew rate cable drivers such as the GS2988.
When this signal is HIGH, the data rate is 270Mb/s. This signal is LOW for all other data
rates.
This signal is also LOW when the device is operating in bypass mode (Auto-bypass and
User-bypass).
The SD/HD signal is LOW when the device is not locked.
GS2985 Multi-Rate SDI Reclocker with Equalization &
De-emphasis
Data Sheet
36663 - 5
July 2012
25 of 45
Proprietary & Confidential