MC144144

The MC144144 is a Line 21 closedcaption decoder for use in television receivers or settop decoders conforming to the NTSC standard. Capability for processing and displaying all of the latest standard Line 21 closedcaption format transmissions is included. The device requires a closedcaption encoded composite video signal, a horizontal sync signal, and an external keyer to produce captioned video. RGB and box signal outputs are provided, which along with the mode select, allow simple interfacing to either color or blackandwhite TV receivers.

Display storage is accomplished with an onchip RAM. A modified ASCII character set, which includes several non English characters, is decoded by an onchip ROM. An onscreen character appears as a white or colored dot matrix on a black background.

Captions (videorelated information) can be up to four rows appearing anywhere on the screen and can be displayed in two modes: rollup, painton, or popon. With rollup captions, the row scrolls up and new information appears at the bottom row each time a carriage return is received. Popon captions work with two memories. One memory is displayed while the other is used to accumulate new data. A special command causes the information to be exchanged in the two memories, thus causing the entire caption to appear at once.

When text (nonvideo related information) is displayed, the rows contain a maximum of 32 characters over a black box which overwrites the screen. Fifteen rows of characters are displayed in the text mode.

An onchip processor controls the manipulation of data for storage and display. Also controlled are the loading, addressing, and clearing of the display RAM. The processor transfers the data received to the RAM during scan lines 21 through 42. The operation of the display RAM, character ROM, and output logic circuits are controlled during scan lines 43 through 237. The functions of the MC144144 are controlled via a serial port which may be configured to be either I²C or SPI.