MICROTRONIX DX-2200-SW-02, User Manual

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DX-2200
– Dual-view 2x1 SDI Video Switcher
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EVEL
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ONTROL
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OMMANDS
The Low Level Text Control Commands provide an additional level of control for
text rendering that can improve performance in certain situations.
The DX-2200 text overlay uses two memory buffers where text strings are
converted to a rendered image that is mixed with the output video. At any one
time, one buffer is being mixed with the video and the other is the spare buffer
used to render the next image when the text overlay is changed (eg by the SnV,
SnS, or SnH commands). When these commands are executed they render the
text to an image, swap the two buffers so that the next image is displayed, and
clear the new spare buffer to prepare it for the next update. The Low Level Text
Control Commands provide additional control of the process.
Table 14: Low Level Text Command Codes
Command Code Mode of Operation
Text Overlay Commands
SB
Renders the text to the spare buffer. The buffers are not automatically
exchanged.
SW Swap the overlay buffers and clear the spare buffer
SS
Swap the overlays buffers.
SC Clear the spare buffer
SnU
SnnU
Render only the text for the specified text field to the spare buffer
A
PPLICATION
E
XAMPLE
1
Suppose that it’s necessary to update the text overlay at a specific time. If the S1T
commands have been used to configure the strings, then executing SU will not
take immediate effect because the strings must be rendered to the spare buffer
before the buffer is switched. The time required to render text depends on the
number of characters drawn and the font size and can cause a noticeable delay.
By using the Low Level Text Commands the overlay update can be controlled
more accurately. After setting the text fields with the S1T command, execute SB to
render the text to the spare buffer. This must be done prior to the desired
switching time so that the text has time to render to the spare buffer. At the time
when overlay switching is required, execute SW and the buffers will be switched.
When the output video mode is progressive there is no frame buffering between
the mixer and the output. The overlay change appears in the next frame output
from the DX-2200. For interlaced modes there is additional buffering before the
output and the overlay change will typically appear in the output video 2 frames
later.