GS1671 datasheet(32/130 Pages) SEMTECH

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GS1671 HD/SD SDI Integrated Receiver

Data Sheet

53737 - 2

September 2012

32 of 130

Once a valid input signal has been detected, the asynchronous lock algorithm enters a

“hunt” phase, in which the device attempts to detect the presence of either TRS words or

DVB-ASI sync words.

By default, the device powers up in auto mode (the AUTO/MAN bit in the host interface

is set HIGH). In this mode, the device operating frequency toggles between HD and SD

rates as it attempts to lock to the incoming data rate. The PCLK output continues to

operate, and the frequency may switch between 148.5MHz, 74.25MHz, 27MHz and

13.5MHz.

When the device is operating in manual mode (AUTO/MAN bit in the host interface is

LOW), the operating frequency needs to be set through the host interface using the

RATE_DET bit. In this mode, the asynchronous lock algorithm does not toggle the

operating rate of the device and attempts to lock within a single standard. Lock is

achieved within three lines of the selected standard.

4.6.2 Signal Interruption

The device tolerates a signal interruption of up to 10

μs without unlocking, as long as no

TRS words are deleted by this interruption. If a signal interruption of greater than 10

μs

is detected, the lock detection algorithm may lose the current data rate, and LOCKED

will de-assert until the data rate is re-acquired by the lock detection block.

4.7 SMPTE Functionality

4.7.1 Descrambling and Word Alignment

The GS1671 performs NRZI to NRZ decoding and data descrambling according to

SMPTE 292/SMPTE 259M-C and word aligns the data to TRS sync words.

When operating in manual mode (AUTO/MAN = LOW), the device only carries out

SMPTE decoding, descrambling and word alignment when the SMPTE_BYPASS pin is set

HIGH and the DVB_ASI pin is set LOW.

When operating in Auto mode (AUTO/MAN = HIGH), the GS1671 carries out

descrambling and word alignment to enable the detection of TRS sync words. When two

consecutive valid TRS words (SAV and EAV), with the same bit alignment have been

detected, the device word-aligns the data to the TRS ID words.

TRS ID word detection is a continuous process. The device remains in SMPTE mode until

TRS ID words fail to be detected.

NOTE: Both 8-bit and 10-bit TRS headers are identified by the device.

GS1671 Datasheet(PDF) 32 Page - Semtech Corporation