SAA7108AE PHILIPS [NXP Semiconductors], SAA7108AE Datasheet - Page 24

• Manufacturer Part Number: SAA7108AE
• Description: HD-CODEC
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
8.17
The pattern generator provides an appropriate
synchronization pattern for the video data path in auxiliary
monitor or HDTV mode, respectively. It provides maximum
flexibility in terms of raster generation for all interlaced and
non-interlaced computer graphics or ATSC formats. The
sync engine is capable of providing a combination of
event-value pairs which can be used to insert certain
values at specified times in the outgoing data stream. It
can also be used to generate digital signals associated
with time events. They can be used as digital horizontal
and vertical synchronization signals on pins HSM_CSYNC
and VSM.
The picture position is adjustable through the
programmable relationship between the sync pulses and
the video contents.
The generation of embedded analog sync pulses is bound
to a number of events which can be defined for a line.
Several of these line timing definitions can exist in parallel.
For the final sync raster composition a certain sequence of
lines with different sync event properties has to be defined.
The sequence specifies a series of line types and the
number of occurrences of this specific line type. After the
sequence has been completed, it restarts from the
beginning. All pulse shapes are filtered internally in order
to avoid ringing after analog post filters.
The sequence of the generated pulse stream must fit
precisely to the incoming data stream in terms of the total
number of pixels per line and lines per frame.
The sync engines flexibility is achieved by using a
sequence of linked lists carrying the properties for the
image, the lines as well as fractions of lines. Figure 11
illustrates the context between the various tables.
The first table serves as an array to hold the correct
sequence of lines composing the synchronization raster. It
can contain up to 16 entries. Each entry holds a 4-bit index
to the next table and a 10-bit counter value which specifies
how often this particular line is invoked. If the necessary
line count for a particular line exceeds the 10 bits, it has to
use two table entries.
The 4-bit index in the line count array points to the line type
array. It holds up to 15 entries where, index 0 is not used,
index 1 points to the first entry, index 2 to the second entry
of the line type array etc.
Each entry of the line type array can hold up to 8 index
pointers to another table. These indices point to portions of
a line pulse pattern: A line could be split up e.g. into a sync,
a blank, and an active portion followed by another blank
portion, occupying four entries in one table line.
2004 Jun 29
HD-CODEC
Pattern generator for HD sync pulses
24
Each index of this table points to a particular line of the
next table in the linked list. This table is called the line
pattern array and each of the up to seven entries stores up
to four pairs of a duration in pixel clock cycles and an index
to a value table. The table entries are used to define
portions of a line representing a certain value for a certain
number of clock cycles.
The value specified in this table is actually another 3-bit
index into a value array which can hold up to eight 8-bit
values. If bit 4 (MSB) of the index is logic 1, the value is
inserted into the G or Y signal only; if bit 4 = 0, the
associated value is inserted into all three signals.
Two additional bits of the entries in the value array (LSBs
of the second byte) determine if the associated events
appear as a digital pulse on the HSM_CSYNC and/or VSM
outputs.
To ease the trigger set-up for the sync generation module,
a set of registers is provided to set up the screen raster
defined as width and height. A trigger position can be
specified as an x, y co-ordinate within the overall
dimensions of the screen raster. If the x, y counter
matches the specified co-ordinates, a trigger pulse is
generated which pre-loads the tables with their initial
values.
Table 6 outlines an example on how to set up the sync
tables for a 1080i HD raster.
Important note:
Due to a problem in the programming interface, writing to
the line pattern array (address D2) might destroy the data
of the line type array (address D1). A work around is to
write the line pattern array data before writing the line type
array. Reading of the arrays is possible but all address
pointers must be initialized before the next write operation.
SAA7108AE; SAA7109AE
Product specification