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参数资料
| 型号： | MC144144P |
| 厂商： | MOTOROLA INC |
| 元件分类： | 颜色信号转换 |
| 英文描述： | Digital Signal Processors 44-JLCC -55 to 125 |
| 中文描述： | COLOR SIGNAL DECODER, PDIP18 |
| 封装： | PLASTIC, DIP-18 |
| 文件页数： | 10/44页 |
| 文件大小： | 565K |
| 代理商： | MC144144P |
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MC144144
10
MOTOROLA
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
μ
s 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
μ
s after the leading
edge of H. The default setting of the MC144144 places the
center of the box at about 13.5
μ
s 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
μ
s, also centered on the
screen, resulting in a leading and trailing 1.32
μ
s 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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