z86131 ZiLOG Semiconductor, z86131 Datasheet - Page 18

• Manufacturer Part Number: z86131
• Description: Ntsc Line 21 Decoder
• Manufacturer: ZiLOG Semiconductor

Z86129/130/131
NTSC Line 21 Decoder
Z86129/130/131 FUNCTIONAL DESCRIPTION (Continued)
Text Mode Display (Z86129 Only)
When TEXT mode is selected, a black box is displayed as
long as valid Line 21 code in the field selected is being de-
tected. The Z86129 provides the option to make the box
blue instead of black. This option holds for Captions as well
as Text.
The default TEXT display mode uses a 15 row by 34 char-
acter black box. TEXT characters are displayed as they are
received starting in the top row. Successive carriage returns
move the display down successive rows until all 15 rows
have been displayed. Thereafter, the text scrolls up as new
characters are added to the bottom row.
If the data for the selected channel is interrupted by a com-
mand for another channel, data processing stops, but the dis-
play remains. When a Resume Text command is received,
data processing resumes and the new characters are added
starting at the position that the display row/column pointer
was in at the interruption of data processing. If a Start Text
command is received, the display is cleared and new char-
acters are displayed starting in row 1, column 1 (left side).
The number of display rows and the location (base row) of
the TEXT box, can be altered by the user. In this way, the
user can decide how much of the screen can be covered
when displaying non-program related information.
When scrolling, the display shifts one scan line per frame
until a complete row has been scrolled. If a carriage return
is received before scrolling is complete, the display imme-
diately completes the “scroll” by jumping up the remaining
scan lines and start displaying the new text.
Caption Mode Display (Z86129 Only)
According to the FCC specifications Caption data can ap-
pear in any of the 15 display rows but a single caption may
consist of no more than 4 rows. The form of the caption dis-
play depends on the caption mode indicated by the trans-
mitted caption command, Pop-on, Paint-on or Roll-up. The
Z86129 can display a single caption having as many as eight
rows. When any of the CAPTION display modes have been
selected, the screen is transparent. (Display box is only
present when a caption is being displayed.)
Pop-on captions work with two caption memories. One of
them is normally displayed while the other is being used to
accumulate new caption data. A new caption is popped-on
by swapping the two memories with the End Of Caption
(EOC) command. When the on-screen memory is erased,
the screen is blank (transparent) and the memory defaults
to the row/column pointer at row 1, column 1 and mono-
chrome non-underlined.
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P R E L I M I N A R Y
When caption mode is selected, the decoder processes any
data following the Resume Caption Loading (RCL) com-
mand (or the EOC). Normally, this command is followed
by a Preamble Address Code (PAC) to indicate the row, col-
umn and character attributes to be used with the following
data. If no PAC is received, the data is added to the location
most recently indicated by the row/column pointer prior to
the receipt of the RCL command.
Paint-on caption mode is essentially equivalent to the Pop-
on mode except that the data received after the Resume Di-
rect Captioning (RDC) command is written to the on-screen
memory rather than the off-screen memory. All the rules
for PACs, Midcodes, and so on, are otherwise the same.
Roll-up caption mode presents a “text” like display that is
limited to 2, 3 or 4 rows, depending on the Resume Roll-
up (RUn) command used. The PAC following the RUn
command is used as the BASE ROW for the ROLL-UP dis-
play. The BASE ROW is the “bottom” row of the ROLL-
UP display. In this case, the black box does not appear until
characters are being displayed and the box is only wide
enough to provide a leading and trailing box in each line.
The new data appears in the bottom row and as each carriage
return is received, the row scrolls up and the new data added
to the bottom. When the number of rows indicated by the
Resume command has been reached, the data in the top row
scrolls off as new data is added to the bottom.
The TAB (INDENT) PAC permits placing Captions start-
ing at 4 character boundaries in any caption row. The TAB
OFFSET command provides the means for adjusting the
starting position for a Caption at any column position in the
current row.
XDS Display Modes (Z86129 Only)
Two preprogrammed XDS display modes are provided.
One provides information about the current program that
would be of interest for “channel grazing”. The second dis-
play shows the grazing packets plus additional XDS packets
which inform the viewer about the program content. Infor-
mation is displayed as it is received. The displays use drop
shadow mode with 15 scan lines per row.
The XDSG mode is the GRAZE (channel grazing) display
(Figure 10). The display contains three rows of information
at the top of the screen, formatted for easy reading. They
contain the following XDS packet information:
OSD Row 1
OSD Row 2
OSD Row 3
Network Name, Call Letters (Green)
Program Name (Italics, Underline, White)
Program Length, Time In Show (Cyan)
DS007200-TVX0199
ZiLOG