cx25870 Conexant Systems, Inc., cx25870 Datasheet - Page 101

• Manufacturer Part Number: cx25870
• Description: Video Encoder With Adaptive Flicker Filtering And Hdtv Output
• Manufacturer: Conexant Systems, Inc.

CX25870/871
Flicker-Free Video Encoder with Ultrascale Technology
1.3.45 VGA(RGB)—DAC Output Operation
Table 1-29. Serial Writes Required to Switch CX25870/871 into VGA/DAC Output Operation
100381B
SLAVER
EN_XCLK
SETUP
OUT_MODE[1:0]
DAC_DISD
Bit Name
Bit 5–Register 0xBA
Bit 7–Register 0xA0
Bit 1–Register 0xA2
Bits 3:2–Register D6
Bit 3–Register 0xBA
Location
In this mode of operation, the CX25870/871 acts as a general-purpose triple
high-speed D/A converter used to drive video receivers, such as PC monitors. The
encoder accomplishes this by bypassing most of the encoder blocks utilized for
television outputs, such as the Flicker Filter and FIFO and routing the RGB or
YCrCb digital data straight through to the on-chip 10-bit DACs. Once the data
arrives at the DACs, it is quickly converted to a set of 700 mV peak-to-peak
analog outputs, streamed through the respective DAC_X output pins, and routed
onto the rest of the graphics system according to the PCB layout.
DACs are terminated into appropriate resistive loads to produce voltage outputs.
The chip’s DAC outputs are specifically designed to produce video output levels
with a total peak-peak active-region amplitude of 700 mV when directly
connected to a single-ended, doubly terminated (Req = 37.5
recommended loading of two 75
transmitting and receiving side), the full-scale video amplitude is from 286 mV
(blanking) to 986 mV (maximum luminance) and synchronization pulses from
0 mV (negative sync tip) to 286 mV (blanking) respectively. The analog
synchronization pulse is generated by the CX25870/871 every time it receives a
falling edge on either the HSYNC* or the VSYNC* input by default. These sync
pulses can be disabled for the RGB outputs by following the steps found in
Table
television outputs depending on the state of the PAL pin. To switch the device into
VGA-DAC Output Mode with bilevel syncs embedded on every Red/Green/Blue
(RGB) analog output, perform the sequence of serial writes found in
only.
Optimal performance is achieved when the CX25870/871’s current controlled
On power-up, the CX25870/871 will output NTSC or PAL standard-definition
1-30.
Value
Conexant
11
1
1
0
1
Ensures CX25871 in slave or pseudo-master interface
CLKI used as pixel clock source.
Setup off. The +56 mV pedestal setup is disabled for active
video lines.
Video [0-3] = 11 = VGA Output Mode:
Disables DACD output. Current is set to 0 mA. Output
voltage goes to 0 V.
DAC_A = Video[0] = Red
DAC_B = Video[1] = Green
DAC_C = Video[2] = Blue
"
± 1 percent resistors (one each for the
Comment
1.0 Functional Description
"
1.3 Device Description
) load. With the
Table 1-29
1-85