12 color bar generator – Cirrus Logic CS4955 User Manual
Page 26
CS4954 CS4955
26
DS278F6
order to maintain the strict timing requirements of
the teletext standard.
shows how to program the TTXHS register
for teletext instantiation into the analog signals for
the various supported TV formats. TTXHS is the
time between the leading edge of the HSYNC sig-
nal and the rising edge of the first TTXRQ signal
and consists of multiples of 27 MHz clock cycles
Note that with increasing values of TTXHS the
time t
TTX
increases as well. The time t
FD
accounts
for the internal pipeline delay due to processing,
synchronization and instantiation of the teletext
data. The time t
PD
is dependant on the TTXHD
register.
Note that the teletext databits are shaped according
to the ITU R.BT653-2 specifications.
If register 0×31 bit 3 is set, (TTX_WINDOW=1)
the teletext is in windows mode. In this mode, the
request pulses become a window where the bit pro-
vided on the TTXDAT pin is valid (see Figure
).
In pulse mode (where the number of request pulses
are determined by the teletext standard chosen), the
length of the window must be programmed by the
user independent of the teletext standard used. The
length of the window is programmed through reg-
ister 0×29 TTXHS (start of window), register
0×2A (TTXHD) and register 0×31 (end of win-
dow). The end-of-window register is a 11 bit value.
In teletext window mode, the TTXHS value can be
selected using the values in Table
these values may need to be adjusted to match your
system delay, use the following equation to com-
pute the TTXHD value:
TTXHS + 1402 = TTXHD (for Europe)
TTXHS + 1151 = TTXHD (for WST)
TTXHS + 1122 = TTXHD (for NABTS)
5.12 Color Bar Generator
The CS4954/5 is equipped with a color bar genera-
tor that is enabled through the CBAR bit of the
CONTROL_1 Register. The color bar generator
works in Master or Slave Mode and has no effect
on the video input/output timing. If the CS4954/5 is
configured for Slave Mode color bars, proper video
timing must be present on the HSYNC and
VSYNC pins for the color bars to be displayed.
Given proper Slave Mode input timing or Master
Mode timing, the color bar generator will override
the video input pixel data.
The output of the color bar generator is instantiated
after the chroma interpolation filter and before the
luma delay line. The generated color bar numbers
are for 100% amplitude, 100% saturation NTSC
EIA color bars or 100% amplitude, 100% satura-
tion PAL EBU color bars. For PAL color bars, the
CS4954/5 generates NTSC color bar values, which
are very close to standard PAL values. The exact
luma and chroma values are listed in Table
TV standard
Teletext
standard
TTXHS
(register
value)
t
TTX
NTSC-M
NABTS
161
10.5
μs
NTSC-M
WST-NTSC
142
9.8
μs
PAL-B
Europe TTX
204
12.0
μs
PAL-B
WST-PAL
163
10.5
μs
PAL-M
NABTS
161
10.5
μs
PAL-M
WST-NTSC
142
9.8
μs
PAL-N (non Arg.)
Europe TTX
204
12.0
μs
PAL-N (non Arg.)
WST-PAL
163
10.5
μs
PAL-N (Arg.)
Europe TTX
204
12.0
μs
PAL-N (Arg.)
WST-PAL
163
10.5
μs
Table 5. Teletext timing parameters