TABLE 5. Character ROM Read Data

Register

Address

D7

D6

D5

D4

D3

D2

D1

D0

Fonts - 2 Color

0x0000–0x2FFE

PIXEL[7:0]

+1

XXXX

PIXEL[11:8]

Fonts - 4 Color

0x3000–0x3FFE

PIXEL[7:0]

+1

XXXX

PIXEL[11:8]

Fonts - 2 Color

0x4000–0x6FFE

PIXEL[7:0]

+1

XXXX

PIXEL[11:8]

Fonts - 4 Color

0x7000–0x7FFE

PIXEL[7:0]

+1

XXXX

PIXEL[11:8]

DISPLAY PAGE RAM

This address range (0x8000–0x81FF) contains the 512 characters which comprise the displayable OSD screens. There must be

at least one End-of-Screen code (0x00) in this range to prevent unpredictable behaviour. NOTE: To avoid any unpredictable

behaviour, this range should be cleared by writinga0tobit3ofthe FRMCTRL1 Register, 0x8400, immediately after power up.

There may also be one or more pairs of End-of-Line and Skip Line codes. The codes and characters are written as 8 bit bytes

but are stored with their attributes in groups of 12 bits. When writing, one byte describes a displayed character (CC), Attribute

Code (AC), End-of-Screen (EOS), End-of-Line (EOL) or Skip Line (SL) code. The type of code is determined by the write

sequence, which must conform to the allowable sequences shown in Table 6. To simplify the table, CC represents one or more

character codes in sequence. A single write operation is enclosed in brackets [], and the both bytes of the Page Ram Address are

shown as one symbol, ADDR.

TABLE 6. Page RAM Write Sequences

OSD Image Consists of

Write Sequence(s)

One Line of Characters Only.

[ADDR-AC-SL-CC-EOS]

One Line of Characters with Attribute Change.

[ADDR-AC-SL-CC] [ADDR-AC-CC-EOS]

Two Lines of Characters with one Attribute.

[ADDR-AC-SL-CC-EOL-SL-CC-EOS]

Two Lines of Characters Separated with Skip Line.

[ADDR-AC-SL-CC-EOL-AC-SL-EOL-AC-SL-CC-EOS]

Two Lines of Characters, each with its own Attribute.

[ADDR-AC-SL-CC-EOL] [ADDR-AC-SL-CC-EOS]

Changing a Character String in a Displayed Screen.

[ADDR-AC-CC]

Changing Only an Attribute in a Displayed Screen.

[ADDR-CC] (CC is the currently displayed character)

When reading characters from RAM, bit 1 of the Character Font Access Register (0x8402) determines whether the character

code or its attribute code is returned. Table 7 gives the character code format read when bit 1 of the Character Font Access

Register is a 0. Table 8 gives the attribute format read when this bit is set to a 1.

TABLE 7. Page RAM Character Read Data

Address Range

D7

D6

D5

D4

D3

D2

D1

D0

0x8000–0x81FF

CHAR_CODE[7:0]

TABLE 8. Page RAM Attribute Read Data

Address

D7

D6

D5

D4

D3

D2

D1

D0

0x8000–0x81FF

xxxx

ATTR_CODE[3:0]

RAM DATA FORMAT

Each of the 512 locations in the page RAM is comprised of a 12-bit code consisting of an 8-bit character or control code, and a

4-bit attribute code. Each of the characters are stored in sequence in the page RAM in bits 7:0. Special codes are used between

lines to show where one line ends and the next begins, and also to allow blank (or “skipped”) single scan lines to be added

between character lines. Table 9 shows the format of a character stored in RAM. Note that even though this is a 12 bit format,

reading and writing characters and codes is done in 8 bytes.

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