ST92196A datasheet(114/268 Pages) STMICROELECTRONICS

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- ON SCREEN DISPLAY CONTROLLER (OSD)

8.5 ON SCREEN DISPLAY CONTROLLER (OSD)

8.5.1 Introduction

The OSD displays Closed Captioning (EIA708

specification) or other character data and menus

on a TV screen.

Each row can be defined through three different

Display configurations:

– Serial mode: each character is defined by an 8-

bit word which provides the character address

into the Font ROM memory. Some codes are re-

served for color controls and do not address any

character description. They are displayed as

spaces and as a direct consequence are active

on a “word” basis. This mode fully supports the

Closed Captioning format.

– Basic parallel mode: each character is defined

by a 16-bit word which provides the character ad-

dress in the Font ROM memory and its color at-

tribute. This mode is called “parallel” as the

colors are definable on a “per character” basis.

– Extended parallel mode: each character is de-

fined by a 24-bit word which provides the charac-

ter address in the Font ROM memory and its

color and shape attributes. This mode is called

“parallel” as the attributes are definable on a “per

character” basis.

8.5.2 General Features

50/60 Hz and 100/120 Hz* operation

525/625 lines operation, 4/3 or 16/9 format

Interlaced or progressive scanning

18x26 or 9x13 character matrix user definable in

ROM. Both matrixes can be mixed.

Up to 63 characters per row

7 character sizes in 18x26, 4 in 9x13

512 possible colors in 4x16-entry palettes

8 levels of translucency on Fast Blanking

Serial

character

mode

supporting

Closed

Captioning format

Basic Parallel Mode for character based color

definition

Extended parallel mode for character based

color and shape definition

Mouse pointer (user definable in ROM)

Rounding,

fringing,

shadowing,

flashing,

scrolling, italics, and various underlining modes

Definition of Terms used in this Chapter

– Pixel: minimum displayed element that the Dis-

play Controller can handle. Its vertical physical

size is always one TV line. Its horizontal physical

size is directly linked to the basic clock frequency

(called Pixel clock) which synchronizes the OSD

and is therefore independent of any magnifica-

tion factor which may be applied to the displayed

element.

– Dot: a dot defines the displayed element which

corresponds to a single bit read from the Font

ROM memory. A dot is represented on the

screen by a "matrix" of pixels. The matrix size de-

pends on the magnification factor applied.

8.5.3 Functional Description

All characters are user definable by masking the

Font ROM content (except the one corresponding

to code 00h which is reserved for test). Two differ-

ent matrixes can be used and mixed:

– 18x26 character matrix

– 9x13 character matrix

The hardware display system has the capability of

displaying one character row and requires the

CPU to update the next display buffer prior to dis-

playing the next row. Using a real time routine, the

On Screen Display supports the display of as

many character rows as the TV screen can physi-

cally handle.

The OSD can display up to 63 characters per row,

depending on the row RAM buffer size (user defin-

able, see Section 8.5.5.1).

The OSD is also designed to handle a mouse

pointer (see Section 8.5.7).

A smart pixel processing unit provides extended

features such as rounding, fringe, or shadowing

for better picture quality. Other smart function such

as flashing, scrolling, italics, underlining and

mouse pointer allow the designing of a high quality

display application.

The screen insertion of the displayed characters is

fully synchronized by the vertical and horizontal

TV synchronizing signals. The OSD controller

generates the Red, Green, Blue and Fast Blanking

video signals through 8-level DAC outputs. The

Fast Blanking video signal can also be generated

as a digital signal if needed.

*Available on some devices

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