ST6380 datasheet(49/82 Pages) STMICROELECTRONICS

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ST6380, ST6381, ST6382, ST6383, ST6388, ST6389

4.8 ON-SCREEN DISPLAY (OSD)

The OSD macrocell is a CMOS LSI character gen-

erator which enables display of characters and

symbols on the TV screen. The character rounding

function enhances the readability of the charac-

ters. The OSD macrocell receives horizontal and

vertical synchronization signal and outputs screen

information via R, G, B and blanking pins.

The main characteristics of the macrocell are list-

ed below

– Number of display characters: 8 lines by 20 col-

umns.

– Number of character types: 192 characters in

one bank.

– Character size: Four character heights (18H,

36H, 54H, 72H), programmable by line.

– Character format: 14x18 dots with character

rounding function.

– Character colour: Eight colours available pro-

grammable by word.

– Display position: 63 horizontal positions pro-

grammable by 2/fOSC and 63 vertical positions

programmable by 4H

– Word spacing: 64 positions programmable from

2/fOSC to 128/fOSC

– Line spacing: 63 positions programmable from 4

to 252 H with two line spacing values per screen.

– Background: No background, square back-

ground or fringe background. The presence of

background is programmable by word, the mode

(fringe or square) being the same for the entire

screen.

– Background colour: Two types selected by word

from a palette of eight colours. The palette is pro-

grammable by screen.

– Display output: Three video signal output termi-

nals (R,G,B) and a blank output terminal.

– Display on/off: Display data may be programmed

on or off by word or entire screen. The entire

screen may be blanked.

– Full screen background: Background on the en-

tire TV screen, one of eight colours available,

with normal text display possible.

4.8.1 Format Specification

The entire display can be turned on or off through

the use of the global enable bit or the display may

be selectively turned on or off by word. To turn off

the entire display, the global enable bit (GE)

should be zero. If the global enable bit and the

OSD ram enable bit are one, the display is control-

led by the word enable bit (WE). The global enable

bit and the OSD ram enable bit are located in the

global enable register and the word enable bit is

located in the space character preceding the word.

Each line must begin with a format character

which describes the format of that line and of the

first word. This character is not displayed.

A space character defines the format of the subse-

quent word. A space character is denoted by a pair

of one in bits 7 (MSB) and 6 of the character regis-

ter in the display RAM. If bit 7 and 6 of a character

character register are used as an index which se-

lects the desired character font from the 192 char-

acters ROM.

The character colour and background can be pro-

grammed by word. This information is encoded in

the space character between words or in the for-

mat character at the beginning of each line. Four

bits define the colour and background of the fol-

lowing word.

Characters are defined in a 14 x 18 dots format.

One dot is defined vertically as 1H (horizontal line)

per field (2H per frame) and horizontally as 1/fOSC

if the smallest character size is enabled. The

rounding function is not available for the smallest

character size. For the other sizes, the rounding

function could be disabled by the rounding disable

bit (RDIS). There is no space between characters

or lines if the vertical space enable (VSE) and hor-

izontal space enable (HSE) bits are both zero.

This allows the use of special graphic characters

(combination of two or more characters).

The normal alphanumeric character set is format-

ted to be 13 x 16 with one empty row at the top and

one at the bottom and one empty column at the

right. If VSE and HSE are both zero, then the

spacing between alphanumeric characters is 1 dot

and the spacing between lines of alphanumeric

characters is 4H per frame.

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