Note that normally the device must first detect the incoming
standard in order for the proper blanking values to be
inserted. However, by setting BLANK_EN low, CLIP_TRS
high and forcing the standard in the HOST write table, the
GS9021 can be used to generate a blank, TRS formatted
video stream (with or without EDH), just by supplying a
clock to the device. The frequency of the clock being
supplied should be less than or equal to the standard
selected. The outgoing stream will just be a frequency
scaled version of that standard.
These three functions can also be turned on individually
through the HOSTIF as described above. THE CLIP_TRS
pin is logically ORed with each of the three bits from the
HOSTIF table. As a result, as long as the CLIP_TRS pin is
asserted, these functions cannot be turned off via the
HOSTIF.
4.6 Ancillary Header
PIN
LOGIC OPR
HOST BIT
ANC_HEADER
4.4 TRS Insertion
PIN
LOGIC OPR
HOST BIT
Updating of the ANC headers can occur to facilitate 8-bit to
10-bit conversion. If the ANC_HEADER bit of the HOSTIF
write table is set HIGH, all 3FC-3FF data values
corresponding to component ANC headers are remapped
to 3FF in the output data stream. For example, if 8 bit data
is input to the device, the ANC header of 00, FF, FF will
appear as 000, 3FC, 3FC and will be remapped to 000, 3FF,
3FF by the GS9021.
TRS_INSERT
TRS words, based on the internal flywheel, can be inserted
into the outgoing data stream by asserting HIGH the
TRS_INSERT bit of the HOSTIF write table. Note that for
proper TRS insertion, the incoming standard must be
detected and the flywheel synchronized. That is, the
GS9021 does NOT provide proper TRS insertion for
unformatted video data (video without TRS words).
5. HOST INTERFACE TABLES
PIN
LOGIC OPR
HOST BIT
In the case where the input signal disappears, TRSs will
continue to be inserted based on the last detected
standard. Further, if a TRS is already in the correct location,
it will be overwritten which may have the effect of correcting
the TRSID word.
HOSTIF_MODE
The HOST INTERFACE TABLES (HOSTIF) refer to memory
locations within the GS9021 which store functional
information about the device. There are two tables, a write
table and read table.
TRS insertion will function incorrectly if the flywheel is
disabled. Thus if the flywheel is disabled the TRS_INSERT
function should be disabled as well.
The write table is organized into 15 word locations (each 8
bits wide) as shown in Table 3 and is used to set various
configuration/flag bits. The read table is organized into 23
word locations (each 8 bits wide) as shown in Table 4 and is
used to read status information from the device.
4.5 Clipping And TRS Blanking/Insertion
PIN
LOGIC OPR
HOST BIT
601_CLIP
CLIP_TRS
OR
The HOSTIF tables can be accessed via an I²C (Inter-
Integrated Circuit) serial interface or an 8-bit parallel
interface. The HOSTIF_MODE pin selects which interface is
used. If the HOSTIF_MODE pin is HIGH, the HOSTIF
operates in I²C mode. If the HOSTIF_MODE pin is LOW, the
HOSTIF operates in parallel mode.
TRS_BLANK
TRS_INSERT
Asserting the CLIP_TRS pin HIGH turns on three features
described previously:
Note that many bits stored in the tables are also available
as device pins. Bits in the write table that have a default
value of 0, are logically ORed with the corresponding pin.
Write table control bits VBLANKS/L and BLANK_EN, which
have a default value of 1, are logically ANDed with the
corresponding pin.
1. ITU-R-601 Clipping,
2. TRS Blanking, and
3. TRS Insertion
If the HOST interface is not going to be used, the best way
to set the related pins is as follows:
HOSTIF_MODE = LOW
15
521 - 65 - 05
GENNUM [ GENNUM CORPORATION ]
