RMV-71 Operations
Copyright illunis LLC, 5/19/2014
Page 73
7.1: On Screen Displays
On Screen Text Display
The OSD function can be used to overlay text data on the live
video image. Two memories are used to store the OSTD data, one
block RAM for the character shape and one Block RAM for the
screen memory. The character memory stores the “pixels” used to
create the character shape. Character shape data is stored from top
to bottom as consecutive bytes, one per line, for a total of 16 lines.
Thus the characters are 8 pixels by 16 lines in size. There are a total
of 128 characters that are mapped to an ASCII Table. Character
shape data is stored in the Microprocessor and loaded into the
FPGA at initialization.
The Screen memory is used to store the “character” that is to be
displayed as 7 bits of data as well as a single bit used to set the
characters background transparency. The screen memory is an ar-
ray of 128 columns by 32 rows. Each entry in the screen memory is
a byte of data that indicates the character index and transparency.
The transparency bit sets the background image to 50% intensity if
set. The character index is coded as a standard ASCII table so that
text can be easily used. The character code is:
The screen memory is accessed through the OSD address regis-
ter. The OSD register contains a bit which indicates which memory
is to be accessed and the address of the character or screen
memory location. To access one of the 128 character memories, as
16 lines of data per character, the OSD address is formatted as a 16-
bit word:
To access one of the screen memory locations, 128 columns
and 32 lines, the OSD address is formatted, with the upper byte as
row address and the lower byte as column address, as a 16-bit word:
Since the OSD text is limited to a 128x32 array of 8x16 bit char-
acters the bitmap of 1024x512 pixels is smaller than the CCD image
area. The OSD Start Register specifies the starting location. The
register format is:
Quick FAQ’s:
►The OSD font is programmable.
►The OSD text is displayed as
8x16 pixel font of 128 characters.
►The OSD text is displayed on a
area 128 characters by 32 lines,
The display area can be posi-
tioned in the image.
►Contact illunis for more infor-
mation on how to customize the
OSD functions.
►
Note: Some OSD functions
make extensive use of floating
point calculations. The micro
processor may abort these cal-
culations if an incoming com-
mand packet is detected. The
OSD display may be temporally
invalid if this happens.
Character ‘B’
DATA
0x00
0x00
0x00
0x7E
0x33
0x33
0x33
0x3E
0x33
0x33
0x33
0x33
0x7E
0x00
0x00
0x00
Transparency
Character “Address” = ASCII Code
Bit 7
6
5
4
3
2
1
0
Mem Select
Address
Char Mem
Not used
Character Address
Character
Line
Bit 15 = ‘1’
1
4
1
3
1
2
1
1
1
0
9
8
7
6
5
4
3
2
1
0
Mem Select
Address
Screen Mem
NA
Character Row
Character Column
Bit 15 = ‘0’
1
4
1
3
1
2
1
1
1
0
9
8
7
6
5
4
3
2
1
0
Vertical offset in 16 line increments
Horizontal offset in 16 pixel increments
1
5
1
4
1
3
1
2
1
1
1
0
9
8
7
6
5
4
3
2
1
0
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