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MC144144P bảng dữ liệu(PDF) 10 Page - Motorola, Inc |
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MC144144P bảng dữ liệu(HTML) 10 Page - Motorola, Inc |
10 / 44 page MC144144 MOTOROLA 10 OPERATING CHARACTERISTICS DECODER OPERATION The MC144144 provides full function NTSC, Line 21 per- formance. Input commands are included to enable the de- coder to process and display any of the eight caption/text data channels (CC1, CC2, CC3, CC4, T1, T2, T3, or T4) con- tained in Line 21 of either field of the incoming video. XDS displays can also be selected. ON/OFF commands control the screen displays. When switched to the decoder off (TV) state, incoming data in the selected channel will still be pro- cessed but not displayed. The MC144144 can also be configured to operate with PAL video signals. It will decode information encoded into its VBI in Line 22. The encoded data must conform to the wave- form and command structure defined for NTSC, Line 21 op- eration. DECODER SET–UP VCO Lock The design includes a VCO with stable gain characteristics and good power supply rejection. The internal horizontal and vertical synchronizing circuits provide a high degree of noise immunity. There are options for both horizontal and vertical lock. The VCO can be phase locked either to the horizontal signal derived from the video input signal (VIDEO) or to the externally supplied HIN signal, typically horizontal flyback. HIN lock is used to provide a display having a minimum of observable jitter. This requires an HIN signal derived from the TV display and of the proper polarity. Such a signal is readily available in a television receiver. VIDEO lock mode enables the VCO to lock in phase to the incoming video signal, thus providing good operation in an application where no display related HIN signal is available, such as in a VCR. Timing Timing signals are derived from the VCO for use in the line counting and display circuits. Line counting requires proper identification of the input signal’s vertical pulse. Default op- eration uses the vertical sync signal derived from the video input signal as the source for vertical lock. This method re- sults in locking characteristics having good performance and good noise immunity. In the event that OSD operation is required under condi- tions when no input video is present, it would be necessary to set the MC144144 for VIN lock. In this mode, the vertical tim- ing will be determined from the vertical pulse signal supplied to the VIN pin. The horizontal position of the caption display is determined by the internal timing circuits. A default condition has been established that should result in a well centered display in a typical application. However, since signal delays through video processing circuits can vary between designs, the MC144144 provides the user with the ability to change the default timing. No matter which of the horizontal lock modes is selected, the display horizontal position on the screen can be adjusted in quarter character (330 ns) steps by serial port commands. DISPLAY FORMATS Normal Mode Characters are displayed as white or colored, dot–matrix characters on an opaque background. The box is normally black but the MC144144 can be set to blue by a serial com- mand. The characters are described by a 12–by–18 dot pat- tern within a character cell which is 16 dots wide by 26 dots high per frame. The location of the character luminance with- in the character cell varies from character to character to al- low for the display of lower case letters with descenders. All characters have at least a one dot border of black around each character. Underline is also provided. The character ROM consists of a 12–by–18 dot–matrix pattern per character. Figure 3 shows the character font. Al- ternate rows and columns are read out of each field to pro- duce an interleaved and rounded character. A display row contains a maximum of 32 characters plus a leading and trailing blank box, each a character cell in width, making the overall width of a display row 34 x 8 = 272 dots. Successive display rows are butted together, so that the total display is 195 dots high. The black box (34 character cells wide by 195 dots high) results in a box size of 45.018 µs in width by 195 scan lines in height. Box starts in scan line 43 and extends to scan line 237. Theoretically, the display will be horizontally centered in the video display when box starts 13.2 µs after the leading edge of H. The default setting of the MC144144 places the center of the box at about 13.5 µs to allow for some delay in the normal video path. However, the box horizontal position can be adjusted by the user in 330 ns increments. The dis- play will be approximately within the safe title area for NTSC receivers. Character width is 42.37 µs, also centered on the screen, resulting in a leading and trailing 1.32 µs black bor- der. An optional caption display mode, drop shadow, can be selected by the user through the serial port. This display mode eliminates the black box around the characters and places a two–dot black shadow to the right and below the character luminance dots when in the 15 scan line per row mode. This display mode is usable in captions, text, and OSD displays. Figure 4 shows the characters with shadow- ing added. Extended Features EIA–608 defined new extended features such as optional background and foreground display attributes and optional extended characters. The MC144144 will always respond to the extended characters but the extended background/fore- ground response can be controlled by the user. The back- ground and foreground attributes add codes for background colors, black foreground as well as transparent, opaque, and semi–transparent background. The BOX signal output pin will be set into a three–state condition whenever one of the semi–transparent attribute codes is active. The external key- ing circuits can then use this condition to implement the in- tended video display. The font for the extended characters is shown in Figure 5. The accented capital letters have been implemented by plac- ing the accent marks above the character cell. When selected, this mode will result in the accent marks being writ- ten into the character cell space of the row above. In some operating modes we will expand the size of the overall box height by adding two additional scan lines at the top and one additional line at the bottom. This will make room for the ac- cent marks in the topmost row and add a black line below the descenders of any lowercase characters in the last row. |
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