ST92196A datasheet(145/268 Pages) STMICROELECTRONICS

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- ON SCREEN DISPLAY CONTROLLER (OSD)

OSD CONTROLLER (Cont’d)

8.5.8.5 Serial Mode

In serial mode, only 1 byte is used to describe the

character code or the attribute (Figure 59):

– If the most significant bit (Bit 7) of this byte is 0,

the byte represents a character code.

– If the most significant bit (Bit 7) of this byte is 1,

the byte represents a serial attribute. Then the

display controller uses Bit 6 to determine wheth-

er the attribute is a foreground serial attribute (Bit

6 = 0) or a background serial attribute (Bit 6 = 1).

A consequence of this structure is that in serial

mode, only the first 128 characters stored in the

font ROM can be accessed (the value of the 7

least significant bits of the character code = the

character number in font ROM).

The first two bytes of the row buffer describing the

row are displayed as border color. The first char-

acter to be displayed in serial mode is in fact the

3rd of the row buffer.

All the attributes (background and foreground) are

displayed as space with background color.

Let’s assume that the start address of the current

row buffer is 2p (even address).

In this case the character codes and attributes are

stored in the OSDRAM at the address 2p+5+z,

where z value is 1 to RCN (RCN is the row charac-

ter count defined in Section 8.5.8.2).

Character Code in Serial Mode

Address in Segment 22h: 2p + 5 + z. See Figure

59.

Bits 6:0 = CHC[6:0]

Character Code in serial

mode

The CHC[6:0] value points to one of the first 128

characters stored in the font ROM.

BACKGROUND SERIAL ATTRIBUTE

Address in Segment 22h: 2p + 5 + z. See Figure

59.

Bits 5:4 Reserved

Bits 3:0 = BP[3:0]

Background Palette pointer

The BP[3:0] value points to one of the 16 prede-

fined entries of the background palette for the

background color and the translucency.

For example, BP[3:0] = 0 points to the first back-

ground palette entry, 30h & 31h if the palette swap

bit PASW of the OSDDR register is reset (see reg-

isters description for more details).

Note: the display of the background serial attribute

is affected by the use of the Italics (see the fore-

ground serial attribute) and also by the “M” bit lo-

cated in the Background Palette (see Section

8.5.6.4 for further details).

CHC6

CHC5

CHC4

CHC3

CHC2

CHC1 CHC0

BP3

BP2

BP1

BP0

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