ST92196A datasheet(160/268 Pages) STMICROELECTRONICS

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- CLOSED CAPTION DATA SLICER (DS)

8.6 CLOSED CAPTION DATA SLICER (DS)

8.6.1 Introduction

Depending on the ST9 device, one or two Data

Slicers may be available in the MCU (refer the de-

vice feature list and Register map).

Each Data Slicer can extract either

Closed caption data from a composite video

signal broadcast in the EIA-608 format. Used in

conjunction with the OSD, it allows closed

caption information to be displayed on a TV

screen.

Gemstar format data transmitted on one or more

horizontal lines in the vertical blanking interval.

In this format, one line contains 4 bytes of data.

The Data Slicer automatically determines the data

format in the specified line and sets the appropri-

ate flag.

8.6.2 Functional Description

Inputs

CCVIDEO: Composite video signal AC coupled

through a 1µF capacitor.

HSYNC:

Horizontal deflection pulse.

VSYNC:

Vertical deflection pulse.

F_4MHz:

4 MHz clock from frequency

multiplier.

Outputs

IRQ:

Conditional negative edge interrupt

request, connected to a CPU

interrupt channel (See Interrupts

Chapter).

As shown in Figure 67, the Data Slicer accepts the

incoming composite video as an AC coupled sig-

nal through a 1µF capacitor to the CCVIDEO pin.

The OSD synchronization signals and a 4 MHz

crystal derived clock are used in the data slicer

signal extraction logic.

Data extraction can be programmed for a selecta-

ble line in either field for a video signal of ampli-

tude of 2V +/-3dB. The slicing level for data is con-

trolled automatically by hardware.

The output signal DSOUT is high when the input

signal exceeds the level of the reference voltage

Vslice, and low when it is less than Vslice.

The clamp is disabled from the time of detection of

vertical sync in CCVIDEO (a sync pulse wider than

12µs) up to line 28.

Note: For good slicing results, it is advised to set

VDDA >= 5.3V. Remember also that VDDA < VDD

+ 0.3V.

Figure 67. Block Diagram

DATA

PROCESSOR

UP/DOWN

COUNTER

DATA

REGISTERS

STATUS

CLOCK

GENERATOR

CLAMP

Interrupt

4 MHz

(from Frequency Multiplier)

CSYNC

Vref (Black)

Vref (Sync)

CCVIDEO

1µF

Vslice

Vref

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