Ross ADC-8733AC, User Manual, Page: 29 / 60

ADC-8733A User Manual (Iss. 02B) User Controls • 3–5
Notes on Timing Modes
This section briefly summarizes the Timing Modes available on the ADC-8733A.
Line Delay (ADC-8733A and ADC-8733A)
This mode uses the input timing signal to generate the output timing. There is a constant delay
between the input and the output. The reference is not used. This is useful in applications where a
constant delay through the card is required. The minimum delay through the card is given in the
“
ADC-8733A Technical Specifications ” on page 5-2. Output timing can be adjusted from this
minimum delay up to an additional two lines in half-pixel increments. Refer to the section “ 2 -
Horizontal Delay ” on page 4-16 and the section “ 4 - Vertical Delay ” on page 4-17 for details.
Line Sync (ADC-8733A and ADC-8733A-S)
This mode uses the reference to generate the output timing on a line-by-line basis, but uses the
input timing signal to decide when a frame begins.
Whenever a signal is received, the output-timing generator waits for the next falling edge of H
Sync on the reference signal before outputting the received signal. The advantage of this mode is
that as long as all input sources are timed to be on the same line, the output timing stays constant,
regardless of which input is selected. This is very useful in that all sources to the ADC-8733A
(for example, from a routing switcher) only need to be lined up to the same line.
Up to two extra lines of delay can be added to the output in half-pixel increments in this mode.
Threshold Point
A finite amount of time is needed to process an input signal before it can be output. This is called
the minimum delay. In Line Sync operation the start of the input line is delayed beyond the
minimum delay until the start of the next reference line, then it is output. If the input signal’s
timing slips enough, the start of its line will not have enough time to get processed and be output
in time to be aligned with the start of the reference line. This point is called the threshold point.
When the input signal slips to the threshold point the output will be delayed until the next
reference line.
The threshold point is measured as the amount of time the input signal’s line start must lead the
reference’s line start. This is 2 lines plus 38µs.
In addition, there is built in hysteresis so that if an input source is near the threshold point, the
output timing will be constant and will not jump back and forth by a line if the input signal varies
slightly. However, if the input signal is exactly on the threshold point, the output timing may vary
from one power up to the next. In other words, the card may power up with different timing than
the previous time it was powered-up. To avoid this condition, it is recommended to keep the input
signal away from the threshold point. Two microseconds can be considered a safe distance.
Note
— If two input sources are not on the same line, then switching from one
source to the other causes a jump in the output timing by an exact number of lines.
For example, if the two sources are 2.5 lines apart, the output jumps by either 2 or 3
lines depending on the position of the sources with respect to the reference.
Note
— In Line Sync Mode, the falling edge of the incoming video’s Sync should be
kept away from the threshold point.