ST92185B datasheet(88/178 Pages) STMICROELECTRONICS

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ST92185B - ON SCREEN DISPLAY (OSD)

7.4 ON SCREEN DISPLAY (OSD)

7.4.1 Introduction

The OSD displays Teletext or other character data

and menus on a TV screen.

In serial mode, characters are coded on one byte.

The display is fully compliant with the WST Tele-

text level 1.5.

In parallel mode, characters are coded on two

bytes, one byte being the font address (character

code), the second byte being used for attribute

control, which can be combined with the serial at-

tribute capabilities. In this mode, the display meets

a significant part of the WST Teletext level 2 spec-

ification.

In order to save memory resources (reduce sys-

tem cost), two display modes are provided with ei-

ther a page mode display mode (teletext stan-

dard, 26 rows) or a line mode (up to 12 rows) for

non teletext specific menus.

The OSD is seen by the ST9 as a peripheral which

has registers mapped in the Paged Register

space.

The character codes to be displayed are taken

from the TDSRAM memory. They are addressed

by the display with the real time sequencer

through the TDSRAM interface character by char-

acter.

The font ROM contains 512 characters. The stan-

dard European font contains all characters re-

quired to support Eastern and Western European

languages. Each character can be defined by the

user with the OSD Screen/Font Editor. All fonts

(except the G1 mosaic font) are fully definable by

masking the pixel ROM content.

Display is done under control of the ST9 CPU and

the vertical and horizontal TV synchro lines.

The OSD provides the Red, Green, Blue signals

and the Fast Blanking switching signal through

four analog outputs. The three Color outputs use a

3-level DAC which can generate half-intensity col-

ors in addition to the standard saturated colors.

The Display block diagram is shown on Figure 1.

A smart pixel processing unit provides enhanced

features such as rounding or fringe for a better pic-

ture quality. Other smart functions such as true

Scrolling and cursor modes allow designing a high

quality display application.

7.4.2 General Features

Serial Character Mode supporting Teletext level

1.5

Parallel Character Mode for TV character

displays (for example channel selection or

volume control menus)

40 or 80 characters/row

Full Page Mode:

23 rows plus 1 Header and 2 Status Rows

Line Mode:

Up to 12 rows plus 1 Header and 2 Status Rows.

4/3 or 16/9 screen format

Synchronization to TV deflection, by Hsync and

Vsync or Csync.

Box Mode: Display text inside and outside box

solid, transparant or blank

Rounding and Fringing

Cursor Control

Concealing

Scrolling

Semi-transparent mode (text windowing inside

video picture)

Half-Tone mode (reduces video intensity inside

a box)

Normal character size 10 x 10 dots.

Other character sizes available as follows:

(SH: Single Height, SW: Single Width, DH: Double

Height, DW: Double Width, DS: Double Size)

Both Serial and

Parallel Mode

Parallel Display Mode

only

SH x SW = 10 * 10 dots

SH x DW = 10 * 20 dots

DH x SW = 20 * 10 dots

DS=DH x DW = 20 * 20

dots

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