
Character Memory (NVM)
The character memory is a 256-row x 64-byte wide
nonvolatile memory (NVM) that stores the characters or
graphic images, and is factory preloaded with the char-
acters shown in Figure 12. The content of the character
memory is user-programmable through the SPI-com-
patible serial interface. Each row contains the descrip-
tion of a single OSD character. Each character consists
of 12 horizontal x 18 vertical pixels where each pixel is
represented by 2 bits of data having three states: white,
black, or transparent. Thus, each character requires 54
bytes of pixel data (Figure 11).
The NVM requires reading and writing a whole charac-
ter (64 bytes) at a time. This is enabled by an additional
row of memory called the shadow RAM. The 64-byte
temporary shadow RAM contains all the pixel data of a
selected character (CMAH[7:0]) and is used as a buffer
for read and write operations to the NVM (Figure 13).
Accessing the NVM is always through the shadow
RAM, and is thus a two-step process. To write a char-
acter to the NVM, the user first fills the shadow RAM
using 54 8-bit SPI write operations, and then executes
a single shadow RAM write command. Similarly, read-
ing a character’s pixel values requires first reading a
character’s pixel data into the shadow RAM, and then
reading the desired pixel data from the shadow RAM to
the SPI port.
M
Single-Channel Monochrome On-Screen
Display with Integrated EEPROM
______________________________________________________________________________________
17
DISPLAY MEMORY
(TWO, 256 x 16-BIT SRAMs)
0
ADDRESS (8 BIT)
L
B
C
L
B
C
B
L
K
B
L
K
I
N
V
I
N
V
L
B
C
B
L
K
I
N
V
479
29
DISPLAY AREA
(16 ROWS x 30 CHARACTERS)
0
29
450
479
CHARACTER ATTRIBUTE BIT DEFINITIONS:
LBC = LOCAL BACKGROUND CONTROL
BLK = BLINK CONTROL
INV = INVERT CONTROL
X = DON'T CARE
CHARACTER MEMORY
ADDRESS LOW (CMAL)
0
PIXEL DATA ARRANGEMENT IN CHARACTER MEMORY (NVM)
256 ROWS x 64 BYTES EEPROM
0
1
2
51
52
53
61
62
63
0
1
2
51
52
53
61
62
63
12 PIXELS
4 PIXEL VALUES
(1 BYTE)
(SEE FIGURE 11 FOR PIXEL MAP)
CHARACTER
DATA USAGE
(12 x 18 PIXELS)
0
1
2
51
52
53
1
2-BIT PIXEL DEFINITIONS:
00 = BLACK, OPAQUE
10 = WHITE, OPAQUE
X1 = TRANSPARENT (EXTERNAL SYNC MODE)
OR GRAY (INTERNAL SYNC MODE)
DISPLAY MEMORY ADDRESS
(DMAH, DMAL)
DISPLAY MEMORY ADDRESS
(DMAH, DMAL)
ADDRESS (8 BIT)
ADDRESS (8 BIT)
30
59
UNUSED
MEMORY
X X X X X
X X X X X
X X X X X
CHARACTER
ADDRESS (CA)
CHARACTER
ATTRIBUTE
255
0
54
54
53
54
CHARACTER
DATA
CHARACTER MEMORY
ADDRESS HIGH (CMAH)
CHARACTER DATA
ARRANGEMENT IN
DISPLAY MEMORY
(SRAM) 480 ROWS
x 2 BYTES SRAM
63
Figure 10. Definitions of Various Parameters