Z86129 Datasheet, PDF (14/50 Pages) Zilog, Inc. – NTSC LINE 21 DECIDER

Z86129/130/131
NTSC Line 21 Decoder
PRELIMINARY
Z86129/130/131 FUNCTIONAL DESCRIPTION (Continued)
Text Mode Display (Z86129 only)
When TEXT mode is selected, a black box will be
displayed as long as valid Line 21 code in the field selected
is being detected. 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
character black box. TEXT characters will be displayed as
they are received starting in the top row. Successive
carriage returns will move the display down successive
rows until all 15 rows have been displayed. Thereafter, the
text will scroll up as new characters are added to the
bottom row.
If the data for the selected channel is interrupted by a
command for another channel, data processing will stop
but the display will remain. When a Resume Text
command is received, data processing will resume and the
new characters will be 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 will be cleared and new characters will be
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 will shift one scan line per
frame until a complete row has been scrolled. If a carriage
return is received before scrolling is complete, the display
will immediately complete 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
appear in any of the 15 display rows but a single caption
may consist of no more than 4 rows. The form of the
caption display depends on the caption mode indicated by
the transmitted 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 will be 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 will
default to the row/column pointer at row 1, column 1 and
monochrome non-underlined.
When caption mode is selected, the decoder will process
any data following the Resume Caption Loading (RCL)
command (or the EOC). Normally, this command will be
followed by a Preamble Address Code (PAC) to indicate
the row, column and character attributes to be used with
the following data. If no PAC is received the data will be
added to the location last 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
Direct 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
display. The BASE ROW will be 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 starting
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.
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