AD9888
Table XI. Active Hsync Override Settings
Table XVI. Clamp Input Signal Source Settings
Override
Result
External Clamp
Function
0
1
Auto determines the active interface.
Override, Bit 3, determines the active interface.
0
1
Internally Generated Clamp
Externally Provided Clamp Signal
The default for this register is 0.
Active Hsync Select
This bit is used under two conditions. It is used to select
the active Hsync when the override bit is set (Bit 4).
Alternately, it is used to determine the active Hsync when
not overriding but both Hsyncs are detected.
A 0 enables the clamp timing circuitry controlled by
clamp placement and clamp duration. The clamp position
and duration is counted from the trailing edge of Hsync.
0E
3
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 Clamp
Polarity bit (Register 0FH, Bit 6).
Table XII. Active Hsync Select Settings
The power-up default value is External Clamp = 0.
Select
Result
0F
6
Clamp Input Signal Polarity
A bit that determines the polarity of the externally provided
CLAMP signal.
0
1
Hsync Input
Sync-on-Green Input
The default for this register is 0.
Vsync Output Invert
A bit that inverts the polarity of the Vsync output.
Table XIII shows the effect of this option.
Table XVII. Clamp Input Signal Polarity Settings
0E
2
Clamp Polarity
Function
1
0
Active Low
Active High
Table XIII. Vsync Output Polarity Settings
A Logic 1 means the circuit will clamp when
CLAMP is Low, and pass the signal to the ADC
when CLAMP is high.
Setting
SYNC
0
1
Invert
Don’t Invert
A Logic 0 means the circuit will clamp when
CLAMP is High, and pass the signal to the ADC
when CLAMP is low.
The default setting for this register is 0.
0E Active Vsync Override
1
The power-up default value is Clamp Polarity = 1.
This bit is used to override the automatic Vsync selection.
To override, set this bit to Logic 1. When overriding, the
active interface is set via Bit 0 in this register.
0F
5
COAST Select
This bit is used to select the active coast source. The
choices are the coast input pin or Vsync. If Vsync is
selected, the additional decision of using the Vsync input
pin or the output from the sync separator needs to be
made (Register 0EH, Bits 1, 0).
Table XIV. Active Vsync Override Settings
Override
Result
0
1
Auto determines the active Vsync.
Override, Bit 0 determines the active Vsync.
Table XVIII. COAST Source Selection Settings
Select
Result
The default for this register is 0.
Active Vsync Select
This bit is used to select the active Vsync when the over
ride bit is set (Bit 1).
0
1
COAST Input Pin
Vsync (See above text.)
0E
0
The default for this register is 0.
4 COAST Input Polarity Override
This register is used to override the internal circuitry
that determines the polarity of the coast signal going
into the PLL.
0F
Table XV. Active Vsync Select Settings
Select
Result
0
1
Vsync Input
Sync Separator Output
Table XIX. COAST Input Polarity Override Settings
The default for this register is 0.
Clamp Input Signal Source
A bit that determines the source of clamp timing.
Override Bit
Result
0F
7
0
1
COAST Polarity Determined by Chip
COAST Polarity Determined by User
The default for coast polarity override is 0.
–22–
REV. B
ROCHESTER [ Rochester Electronics ]
