Bt860/861
3.0 Digital Processing and Functionality
3.2 Effects
Multiport YCrCb to NTSC/PAL /SECAM
3.2.15 Teletext Operation of Bt860/861
Teletext encoding in the Bt860/861 is accomplished via a two-wire interface,
TTXDAT and TTXREQ, and several control registers, programmed via the serial
programming interface. The Bt860/861 Teletext output conforms to Teletext B
for 625-line systems; Teletext should be disabled for 525-line systems. For more
details on the Teletext standard, consult ITU-R BT.653 or EACEM Technical
Report No. 8.
The TTXDAT pin is the Teletext data insertion pin, and the TTXREQ pin is
the timing pin. The TTXREQ pin can be configured into two Teletext timing
modes by using register bit TXRM (59[1]). Figure 3-16 illustrates Teletext
timing.
Figure 3-16. Teletext Timing
(1)
1
t
Composite or
Luminance (Y)
Output
. . .
Bit 1 2 3 4 5 6 7 8 9
Clock Run-In
(2)
TTXDAT
(4)
2
(3)
t
TTXREQ
(Timing Mode 1)
. . .
8
Bit
1
2
3
4
5
6
7
TTXREQ
(Timing Mode 2)
(5)
t
3
(6)
t
4
HSYNC*
NOTE(S): (unchanged note)
(1)
t is the start of Teletext. The midpoint of the first Teletext pulse is 10.2 µs from the midpoint of the analog horizontal
1
sync pulse falling edge.
(2)
The Teletext data on the TTXDAT pin must observe proper set-up and hold times relative to the Teletext timing clock
falling edge (TTXREQ signal in timing mode 1).
Teletext data is latched on the Teletext timing clock’s falling edge.
(3)
(4)
(5)
The Teletext timing clock’s first rising edge (t ) occurs 335 system clocks after falling HSYNC* for ITU-R BT.601 timing.
2
Placement of the rising edge of the TTXREQ request signal (t ) in Teletext timing mode 2 is definable using register field
3
TXHS[10:0].
(6)
Placement of the falling edge of the TTXREQ request signal (t ) in Teletext timing mode 2 is definable using register field
4
TXHE[10:0].
861_001
D860DSA
Conexant
3-25
CONEXANT [ CONEXANT SYSTEMS, INC ]
