GS1560A/GS1561 Data Sheet
3.7 SMPTE Functionality
The GS1560A/GS1561 is said to be in SMPTE mode once the device has detected
SMPTE TRS sync words and locked to the input data stream as described in Lock
Detect on page 35. The device will remain in SMPTE mode until such time that
SMPTE TRS sync words fail to be detected.
The lock detect block may also drop out of SMPTE mode under the following
conditions:
•
•
•
•
RESET_TRST is asserted LOW
CDx is HIGH
SMPTE_BYPASS is asserted LOW in slave mode
DVB_ASI is asserted HIGH in slave mode
TRS word detection is a continuous process and both 8-bit and 10-bit TRS words
will be identified by the device in both SD and HD modes.
In master mode, the GS1560A/GS1561 sets the SMPTE_BYPASS pin HIGH and
the DVB_ASI pin LOW to indicate that it has locked to a SMPTE input data stream.
When operating in slave mode, the application layer must assert the DVB_ASI pin
LOW and the SMPTE_BYPASS pin HIGH in order to enable SMPTE operation.
3.7.1 SMPTE Descrambling and Word Alignment
After serial-to-parallel conversion, the internal 10-bit or 20-bit data bus is fed to the
SMPTE descramble and word alignment block. The function of this block is to carry
out NRZI-to-NRZ decoding, descrambling according to SMPTE 259M or 292M,
and word alignment of the data to the TRS sync words.
Word alignment occurs when two consecutive valid TRS words (SAV and EAV
inclusive) with the same bit alignment have been detected.
In normal operation, re-synchronization of the word alignment process will only
take place when two consecutive identical TRS word positions have been
detected. When automatic or manual switch line lock handling is 'actioned', (see
Switch Line Lock Handling on page 39), word alignment re-synchronization will
occur on the next received TRS code word.
3.7.2 Internal Flywheel
The GS1560A/GS1561 has an internal flywheel which is used in the generation of
internal / external timing signals, in the detection and correction of certain error
conditions and in automatic video standards detection. It is only operational in
SMPTE mode.
The flywheel consists of a number of counters and comparators operating at video
pixel and video line rates. These counters maintain information about the total line
length, active line length, total number of lines per field / frame, and total active
lines per field / frame for the received video stream.
27360 - 8 September 2005
38 of 80
GENNUM [ GENNUM CORPORATION ]
