ST92196A datasheet(120/268 Pages) STMICROELECTRONICS

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- ON SCREEN DISPLAY CONTROLLER (OSD)

OSD CONTROLLER (Cont’d)

8.5.3.11 Translucency Function

The translucency feature is designed to provide a

better OSD quality while displaying rows in mixed

mode.

Instead of forcing the background color of any

character to any full intensity color, (which will pre-

vent the viewer from seeing a significant amount of

the video picture), or having a fully transparent

background (i.e. no background) which makes the

OSD more difficult to read for the viewer, the trans-

lucency provides a real time mix between both the

video and the OSD background information. This

feature will appear as a “boxing” effect around all

the displayed characters.

The translucency can be handled in two different

ways at application level, depending on the video

processor used in the application.

1. When the video processor accepts an analog

control of the fast switch OSD signal (called

“FB”), the translucency can be handled directly

through the real time amplitude of the FB signal

(refer to Color attribute control for Border, Back-

ground palette and Underline color settings).

2. When the video processor accepts only a digital

FB signal, the translucency function may be im-

plemented on the chassis with the help of an

additional digital output of the MCU, which is

provided as an I/O pin alternate function.

This digital output called “TSLU” is active (set to

“1”) when the OSD displays the Background and

Foreground or when the mute is active (refer to the

description of the LSM[2:0] bits in the OSDMR reg-

ister) and is inactive the rest of the time (during

foreground or if no display), including character

00h.

This TSLU signal is controlled by the TSLE bit in

the OSDER register. When not used, (TSLE=0),

the TSLU signal is held at “1” by hardware.

Application Note

In order to enable the Translucency Function (See

Example No. 2, above), the following procedure

must be performed:

– Fast Blanking must be set to Digital mode. Set bit

DIFB (bit 7) of register OSDBCR1 (R247, page

42) to 1. Refer to Section 8.5.9 Register Descrip-

tion.

– Initialize port 3.0 as a push-pull type Alternate

Function output. Refer to Section 8.5.3 Function-

al Description.

– Set bit TSLE (bit 2) of register OSDER (R248,

page 42) to 1. Refer to Section 8.5.9 Register

Description.

– For the selected colors (i.e. those which will ap-

pear as transparent with contrast reduction), set

bits BT[2:0] to 0. Refer to Section 8.5.6.4 Back-

ground Palettes.

Figure 56. Digital Translucency Output Pin Example

Current displayed video line

TLSU Digital Output

FB (active high)

No Display

Foreground

No Display

Transparent Background

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