Sundance SMT319 - Manual (Page 19)

Version 1.0.7 Page 19 of 45 SMT319 User Manual
Overlay Text & Character Generator
*
A 1k byte memory within the FPGA is able to store a 40x25 screen-full of characters.
Each character may take on any value between 1 and 127. A value of 0 indicates
that the character will not be displayed. A character value with bit 7 (128 to 255) set
indicates that the white character will be displayed within a black square, as opposed
to white on top of the underlying colours.
Figure 4: Text overlay example
The above picture shows white characters overlaid on top of the picture (bit 7 = 0),
and white characters overlaid with a black background (bit 7 = 1).
Mixer *
This simply superimposes the character generator output on top of the normal video
stream.
Video Output Data Control
The Bt864A produces HSYNC and VSYNC signals, which inform the output data and
HPI controllers to fetch and shift out the correct pixel data.
* not available in the first release of the SMT319