1.0 Functional Description
CX25870/871
1.3 Device Description
Flicker-Free Video Encoder with Ultrascale Technology
1.3.31 FIELD Pin Output
Like its predecessor, the Bt868/869, the CX25870/871 includes a FIELD pin
output. This signal is output only and is accessed through pin #37. The frequency
of the FIELD pin is 30 Hz during an NTSC video output, and 25 Hz throughout a
PAL or SECAM video output. The only programming step required to obtain the
FIELD output is to serially write the EN_OUT bit to 1.
The purpose of this signal is to provide a digital TTL compatible output which
tracks the analog interlaced field presently being transmitted by the CX25870/871
DACs. The peak-to-peak amplitude of this output will be from 0 V to the level
present on the VDD_CO and VDDL pins. If these pins are tied to 3.3 V, then the
FIELD high state is transmitted at a 3.3 V level. If these pins are tied to 1.8 V or
lower voltage, then the FIELD high state is transmitted at a 1.8 V or lower level.
The logical 0 level from FIELD will always be GND/VSS regardless of the
logical 1 voltage.
The FIELD output transitions after the rising edge of CLKI, two clock cycles
following the leading edge of the digital HSYNC* input or output. Figure 1-21
shows the relationship between the FIELD and Composite (CVBS) outputs and
VSYNC* input for NTSC. Figure 1-22 illustrates this same relationship for PAL.
Figure 1-21. FIELD Pin Output Timing Diagram (NTSC-M, J, 4.43)
RESET*
Start
of
VSYNC*
Analog
FIELD 1 = ODD
Composite
Output
523
524
525
4
5
6
7
22
1
2
3
8
9
10
FIELD Pin
Output
Analog
FIELD 2 = EVEN
Composite
Output
261
262
263
264
265
266
267
268
269
270
271
272
285
FIELD Pin
Output
*FIELDI Bit = 0
100381_094
1-54
Conexant
100381B
CONEXANT [ CONEXANT SYSTEMS, INC ]
