6-18
Video Interface and On-Screen Display
Final Rev F
Copyright 1996 by LSI Logic Corporation. All rights reserved.
ever, now the device uses an external horizontal sync pulse, rather than
the internally generated signal, to reset the internal horizontal counters,
and uses the transition of an external vertical sync pulse to indicate the
start of a eld. When the external sync master asserts VS and HS within
64 cycles of each other, the eld is an odd eld, otherwise it is an even
eld. Note that the external HS and VS signals must be synchronous to
the SYSCLK signal for reliable operation. For proper operation, the HS
signal must be received every line time, and the VS signal must be
received every eld time
Pixels output from the L64005 in slave mode are based on an internally
generated reference counter with respect to the HS pulse. Users must
therefore make sure that the pixel output from the L64005 is correctly
aligned in time with the expected input into the next device (typically a
composite video encoder or a DAC). Also note that the pixel output in
slave mode remains synchronous to SYSCLK.
6.5.4
Adaptive
Modication of
Video Raster for
Copy Protection
VCR anti-copy schemes rely on the real-time modication of the length
of the vertical blanking interval. When the L64005 is in master mode, the
user may reprogram the vertical blanking interval registers over the user
interface from the attached microprocessor. The vertical timing registers
are therefore double buffered.
6.6
Pan and Scan
Operation
The L64005 implements pan and scan of an image over the display area.
There are two situations where a picture might be panned:
the picture is too large to be displayed in the available screen area
the picture is too small to occupy the entire screen
An example of the rst situation is the decoding of a wide-screen image
(16:9 aspect ratio) that is then displayed on a standard 4:3 aspect ratio
screen. An example of the second situation is low resolution images that
are transmitted as part of a program guide. The small images can be
located anywhere on the screen. The same set of parameters control
both situations.
The Group 6 Registers 2 through 13 indicate the reconstruction
addresses, where the L64005 stores data in memory. If the Pan and
Scan Word Origin Register is zero, the top-left pixel in the reconstructed
image coincides with the rst pixel in the active display area. If bits 5:0