Most television sets built Jan. 1, 2000, and thereafter must include so-called V-chips, a system designed to allow consumers to filter out pro gramming they might find objectionable, using a rating system adopted by the TV industry for violence, language and sexual situations. What is called a V-chip is actually circuitry built into the central processor of the TV set.

1. The Signal

The rating for a television program -- TV-MA, TV-14 and so on -- is sent along as part of the signal from broadcasters or cable operators, who have encoders built into their transmitters.

2. The Set

Analog TV sets can receive some 525 lines of information, which are scanned constantly by an electron gun in the set to produce the picture on the screen. Although depicted here the, first 30 of these 525 lines are not visible -- they are used to transmit such information as data from network affiliates.

3. The Consumer

Sets equipped with V-chips generallly contain on-screen menus to enable consumers to select the ratings they want to block out. The consumer is prompted to select a locking code, a password that will allow the filter to be overridden or modified.

SELECT TV GUIDELINE

(1)TV-Y(Young children)

(2)TV-Y7(Children 7 and over)

(3)TV-G(General Audience)

(4)TV-PG(Parental Guidance)

(5)TV-14(Viewers 14 and over)

(6)TV-MA(Mature audience)

PRESS (1) TO (6) TO SELECT

PRESS (MENU) TO RETURN

4. The Blocking

When the set is on, the central processor checks every three seconds to see if it is supposed to be blocking the programming. If someone tries to select a show that should be blocked, the screen generally is blacked out and display s a message asking for the password.

Line 21 of those 30 lines is reserved for information for individual TV sets -- this is where the rating code for the V-chip is contained (as well as closed captioning).

ENTER 4 DIGIT

PASSCODE (----)

THIS PROGRAMMING EXCEEDS YOUR RATING LIMITS

YOUR TV WILL BE TURNED

OFF UNLESS THE CHANNEL

IS CHANGED OR THE

PASSCODE IS ENTERED

SOURCES: Consumer Electronics Manufacturers Association; Thomson Consumer Electronics