AD9981SLASHPCB datasheet(35/44 Pages) AD

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AD9981

Rev. 0 | Page 35 of 44

Table 43. Input Bandwidth Select

Input Bandwidth

Result

Low analog input bandwidth

High analog input bandwidth

0x1E

Power-Down Control Select

This bit determines whether power-down is con-

trolled manually or automatically by the chip. If

automatic control is selected (Register 0x1E, Bit 4), the

AD9981’s decision is based on the status of the sync

detect bits (Register 0x24, Bits 2, 3, 6, and 7). If either

an Hsync or a sync-on-green input is detected on any

input, the chip powers up or powers down. For

manual control, the AD9981 allows the flexibility of

control through both a dedicated pin and a register bit.

The dedicated pin allows a hardware watchdog circuit

to control power-down, while the register bit allows

power-down to be controlled by software. With

manual power-down control, the polarity of the

powerdown pin must be set (0x1E, Bit 2) whether it is

used or not. If unused, it is recommended to set the

polarity to active high and hardwire the pin to ground

with a 10 kΩ resistor.

Table 44. Auto Power-Down Select

Power-Down Select

Result

Manual power-down control

(User determines power-down)

Auto power-down control

(Chip determines power-down)

0x1E

Power-Down

This bit is used to manually place the chip in power-

down mode. It is only used if manual power-down

control is selected (see Bit 4 above). Both the state of

this register bit and the power-down pin (Pin 17)

are used to control manual power-down. (See the

Power Management section for more details on

power-down.)

Table 45. Power-Down Settings

Power-Down Select

Pin 17

Result

Normal operation

Power-down

0x1E

Power-Down Polarity

This bit defines the polarity of the power-down pin

(Pin 17). It is only used if manual power-down control

is selected (see Bit 4 above).

Table 46. Power-Down Pin Polarity

Select

Result

Power-down pin is active low

Power-down pin is active high

0x1E

Power-Down Fast Switching Control

This bit controls a special fast switching mode. With

this bit the AD9981 can stay active during power-

down and only put the outputs in high impedance.

This option is useful when the data outputs from two

chips are connected on a PCB and the user wants to

switch instantaneously between the two.

Table 47. Power-Down Fast Switching Control

Fast Switching Control

Result

Normal power-down operation

The chip stays powered up and the

outputs are put in high impedance

mode

0x1E

SOGOUT High Impedance Control

This bit controls whether the SOGOUT output pin is

in high impedance or not, when in power-down mode.

In most cases, SOGOUT is not put in high impedance

during normal operation. It is usually needed for sync

detection by the graphics controller. The option to put

SOGOUT in high impedance is included mainly to

allow for factory testing modes.

Table 42. SOGOUT High Impedance Control

SOGOUT Control

Result

The SOGOUT output operates as

normal during power-down.

The SOGOUT output is in high

impedance during power-down.

OUTPUT CONTROL

0x1F

7:5

Output Mode

These bits choose between three options for the

output mode. In 4:4:4 mode, RGB is standard. In 4:2:2

mode, YCbCr is standard, which allows a reduction in

the number of output pins from 30 to 20. In 4:4:4

DDR output mode, the data is in RGB mode, but

changes on every clock edge. The power-up default

setting is 100.

Table 43. Output Mode

Output Mode

Result

100

4:4:4 RGB mode

101

4:2:2 YCbCr mode

110

4:4:4 DDR mode

0x1F

Primary Output Enable

This bit places the primary output in active or high

impedance mode. The power-up default setting is 1.

Table 44. Primary Output Enable

Select

Result

Primary output is in high impedance

mode

Primary output is enabled

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