Z86129 Datasheet, PDF (9/50 Pages) Zilog, Inc. – NTSC LINE 21 DECIDER

PRELIMINARY
Z86129/130/131
NTSC Line 21 Decoder
The SPI mode is a three wire bus with the Z86129/130/131 _{Voltage/Current Reference}
performing as the slave device. Communication is
synchronized by the SCK signal generated by the master.
Typically, the serial data output is transmitted on the falling
edge of SCK and the received data is captured on the
rising edge of SCK. All data is exchanged as 8-bit bytes.
The Voltage/Current reference circuit uses an externally
connected resistor to establish the reference levels that
are used throughout the Z86129/130/131. The use of an
external resistor provides improved internal precision at
minimal additional cost.
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Z86129/130/131 FUNCTIONAL DESCRIPTION
The Z86129 provides full function NTSC, Line 21
performance. Input commands are included to enable the
decoder to process and display any of the eight
Caption/Text data channels (CC1, CC2, CC3, CC4, T1,
T2, T3 or T4) contained in Line 21 of either field of the
incoming video. XDS data can also be selected for display.
The DECODER ON/OFF commands control whether or
not the Line 21 data in the selected channel is actually
displayed. When switched to the DECODER OFF (TV)
state, incoming data in the selected channel will still be
processed but not displayed.
The Z86129/130/131 can also be configured to operate
with PAL or SECAM video signals. It will decode
information encoded into its VBI in Line 22. The encoded
data must conform to the waveform and command
structure defined for NTSC Line 21 operation.
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.
Video 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 operation uses the vertical sync signal derived
from the video input signal as the source for vertical lock.
This method results in locking characteristics having good
performance and good noise immunity.
In the event that OSD operation is required under
conditions when no input video is present, it would be
necessary to set the Z86129 for VIN lock. In this mode, the
vertical timing 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
Z86129 provides the user with the ability to change the
default timing. No matter which of the horizontal lock
modes are selected, the display horizontal position on the
screen can be adjusted in quarter character (330 ns) steps
by serial port commands.
Displayable Character Set (Z86129 only)
Normal Mode. Characters are displayed as white or
colored dot matrix characters on an opaque background.
The Box is normally black but the Z86129 can be set to a
blue background Box with a serial command. The
characters are described by a 12 by 18 dot pattern within
a character cell which is 16 dots wide by 26 dots high per
frame. The location of the character luminance within the
character cell varies from character to character to allow
for the display of lower case letters with descenders. All
characters have at least a 1-dot border of black around
each character. Underline is also provided. Figure 4 shows
the Z86129 standard character map and font.
The character ROM consists of a 12 by 18 dot matrix
pattern per character. Figure 5 shows the character font.
Alternate rows and columns are read out in each field to
produce an interleaved and rounded character. A display
row contains a maximum of 32 characters plus a leading
and trailing black 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 occupies 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. The Box starts in scan line 43 and extends to
scan line 237. Theoretically, the display will be horizontally
centered in the video display when the Box starts 13.2 µs
after the leading edge of H.
DS96TEL0200
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