AD9887SLASHPCB datasheet(31/40 Pages) AD

31 / 40 page

REV. 0

AD9887

–31–

When DEMUX = 0, this bit is ignored as data always

comes out of only Port A.

HSYNC Output Polarity

One bit that determines the polarity of the HSYNC out-

put and the SOG output. Table XV shows the effect of

this option. SYNC indicates the logic state of the sync pulse.

Table XV. HSYNC Output Polarity Settings

Setting

SYNC

Logic 1 (Positive Polarity)

Logic 0 (Negative Polarity)

The default setting for this register is 1. (This option

works on both the analog and digital interfaces.)

VSYNC Output Invert

One bit that inverts the polarity of the VSYNC output.

Table XVI shows the effect of this option.

Table XVI. VSYNC Output Polarity Settings

Setting

VSYNC Output

Invert

No Invert

The default setting for this register is 1. (This option

works on both the analog and digital interfaces.)

HSYNC Input Polarity

A bit that must be set to indicate the polarity of the HSYNC

signal that is applied to the PLL HSYNC input.

Table XVII. HSYNC Input Polarity Settings

HSPOL

Function

Active LOW

Active HIGH

Active LOW is the traditional negative-going Hsync pulse.

All timing is based on the leading edge of Hsync, which is

the FALLING edge. The rising edge has no effect.

Active HIGH is inverted from the traditional Hsync, with a

positive-going pulse. This means that timing will be based on

the leading edge of Hsync, which is now the RISING edge.

The device will operate if this bit is set incorrectly, but the

internally generated clamp position, as established by

CLPOS, will not be placed as expected, which may gener-

ate clamping errors.

The power-up default value is HSPOL = 1.

6 COAST Input Polarity

A bit to indicate the polarity of the COAST signal that is

applied to the PLL COAST input.

Table XVIII. COAST Input Polarity Settings

CSTPOL

Function

Active LOW

Active HIGH

Active LOW means that the clock generator will ignore Hsync

inputs when COAST is LOW, and continue operating at the

same nominal frequency until COAST goes HIGH.

Active HIGH means that the clock generator will ignore

Hsync inputs when COAST is HIGH, and continue operat-

ing at the same nominal frequency until COAST goes LOW.

This function needs to be used along with the COAST

polarity override bit (Register 14, Bit 1).

The power-up default value is CSTPOL = 1.

5 Clamp Input Signal Source

A bit that determines the source of clamp timing.

Table XIX. Clamp Input Signal Source Settings

EXTCLMP

Function

Internally-Generated Clamp

Externally-Provided Clamp Signal

A 0 enables the clamp timing circuitry controlled by

CLPLACE and CLDUR. The clamp position and dura-

tion is counted from the leading edge of Hsync.

A 1 enables the external CLAMP input pin. The three

channels are clamped when the CLAMP signal is

active. The polarity of CLAMP is determined by the

CLAMPOL bit.

The power-up default value is EXTCLMP = 0.

CLAMP Input Signal Polarity

A bit that determines the polarity of the externally pro-

vided CLAMP signal.

Table XX. CLAMP Input Signal Polarity Settings

EXTCLMP

Function

Active LOW

Active HIGH

A Logic 0 means that the circuit will clamp when CLAMP

is HIGH, and it will pass the signal to the ADC when

CLAMP is LOW.

A Logic 1 means that the circuit will clamp when CLAMP

is LOW, and it will pass the signal to the ADC when

CLAMP is HIGH.

The power-up default value is CLAMPOL = 1.

3 External Clock Select

A bit that determines the source of the pixel clock.

Table XXI. External Clock Select Settings

EXTCLK

Function

Internally Generated Clock

Externally Provided Clock Signal

A Logic 0 enables the internal PLL that generates the

pixel clock from an externally provided Hsync.

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