ISL51002 datasheet(27/32 Pages) INTERSIL

27 / 32 page

December 22, 2006

channel may look like SOG activity when there actually is no

SOG signal, while non-standard SOG signals and TriLevel

sync signals may have amplitudes below the default SOG

slicer levels and not be easily detected. As a consequence,

not all of the activity detect bits in the ISL51002 are correct

under all conditions.

For best SOG operation, the SOG low pass filter (register

0x04[4] should always be enabled to reject the high

frequency peaking often seen on video signals.

HSYNC and VSYNC Activity Detect

Activity on these bits always indicates valid sync pulses, so

they should have the highest priority and be used even if the

SOG activity bit is also set.

SOG Activity Detect

The SOG activity detect bit monitors the output of the SOG

slicer, looking for 64 consecutive pulses with the same

period and duty cycle. If there is no signal on the Green

(or Y) channel, the SOG slicer will clamp the video to a DC

level and will reject any sporadic noise. There should be no

false positive SOG detects if there is no video on Green

(or Y).

If there is video on Green (or Y) with no valid SOG signal,

the SOG activity detect bit may sometimes report false

positives (it will detect SOG when no SOG is actually

present). This is due to the presence of video with a

repetitive pattern that creates a waveform similar to SOG.

For example, the desktop of a PC operating system is black

during the front porch, horizontal sync, and back porch, then

increases to a larger value for the video portion of the

screen. This creates a repetitive video waveform very similar

to SOG that may falsely trigger the SOG Activity detect bit.

However, in these cases where there is active video without

SOG, the SYNC information will be provided either as

separate H and V sync on HSYNCIN and VSYNCIN, or

composite sync on HSYNCIN. HSYNCIN and VSYNCIN

should therefore be used to qualify SOG. The SOG Active bit

should only be considered valid if HSYNC Activity

Detect = 0. Note: Some pattern generators can output

HSYNC and SOG simultaneously, in which case both the

HSYNC and the SOG activity bits will be set, and valid. Even

in this case, however, the monitor should still choose

HSYNC over SOG.

TriLevel Sync Detect

The TriLevel detect for Sync on Green (SOG) utilizes the

digitized data from the selected Green video channel. If

TriLevel Sync is present, the default DC Clamp start position

will clamp at the top of the TriLevel Sync pulse giving a false

negative for TriLevel detect and clamping off the bottom half

of the green video. If you have an indication of active SOG

you must move the clamp start to a value greater than 0x30

to check to see if the TriLevel Sync is present.

SYNC Output Signals

The ISL51002 has a pair of HSYNC output signals,

HSYNCOUT and VSYNCOUT, and HSOUT.

HSYNCOUT and VSYNCOUT are buffered versions of the

incoming sync signals; no synchronization is done. These

signals are used for mode detection

HSOUT is generated by the ISL51002’s logic and is

synchronized to the output DATACLK and the digital pixel

data on the output databus. HSOUT is used to signal the

start of a new line of digital data.

Both HSYNCOUT and VSYNCOUT (including the sync

separator function) remain active in power-down mode. This

allows them to be used in conjunction with the Sync Status

registers to detect valid video without powering up the

ISL51002.

HSYNCOUT

HSYNCOUT is an unmodified, buffered version of the incoming

HSYNCIN or SOGIN signal of the selected channel, with the

incoming signal’s period, polarity, and width to aid in mode

detection. HSYNCOUT will be the same format as the incoming

sync signal: either horizontal or composite sync. If a SOG input

is selected, HSYNCOUT will output the entire SOG signal,

including the VSYNC portion, pre-/post-equalization pulses if

present, and Macrovision pulses if present. HSYNCOUT

remains active when the ISL51002 is in power-down mode.

HSYNCOUT is generally used for mode detection.

VSYNCOUT

VSYNCOUT is an unmodified, buffered version of the incoming

VSYNCIN signal of the selected channel, with the original

VSYNC period, polarity, and width to aid in mode detection. If a

SOG input is selected, this signal will output the VSYNC signal

extracted by the ISL51002’s sync slicer. Extracted VSYNC will

be the width of the embedded VSYNC pulse plus pre- and post-

equalization pulses (if present). Macrovision pulses from an

NTSC DVD source will lengthen the width of the VSYNC pulse.

Macrovision pulses from other sources (PAL DVD or videotape)

may appear as a second VSYNC pulse encompassing the

width of the Macrovision. See the Macrovision section for more

information. VSYNCOUT (including the sync separator function)

remains active in power-down mode. VSYNCOUT is generally

used for mode detection, start of field detection, and even/odd

field detection.

HSOUT

HSOUT is generated by the ISL51002’s control logic and is

synchronized to the output DATACLK and the digital pixel data

on the output databus. Its trailing edge is aligned with pixel 0. Its

width, in units of pixels, is determined by register 0x2A, and its

polarity is determined by register 0x29[3]. As the width is

increased, the trailing edge stays aligned with pixel 0, while the

leading edge is moved backwards in time relative to pixel 0.

HSOUT is used by the scaler to signal the start of a new line of

pixels.

ISL51002

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