User manual

Imagestore HDTV User Manual Overview
Miranda Technologies Ltd Page 137
Clean switching between the inputs is made possible by buffering the inputs
in line FIFOs to co-time them before processing. The reference timing will
adjust the active depth of the FIFOs to allow for wider timing differences
between the input signals.
The shortest video processing delay from any input through the Imagestore
HDTV to the PGM output is approximately 1us and occurs when the input
line FIFO depth is at its minimum. By increasing the output reference timing
w.r.t (with respect to) the 1/A input the FIFO depth is lengthened up to its
maximum of 1 line.
Timing is dependent on the relative phase between the SDI input and the tri
level sync. To illustrate the set up refer to the following.
This examples deals with a system where the SDI input arrives 3us earlier
than the associated tri level sync . We will call this timing ‘-3us’. If the SDI
were to arrive 5us after the tri level sync the timing would be ‘+5us’.
To set the minimum SDI delay through the unit of 1us:
As 1/A is 3us earlier than the tri level sync and PGM is at least 1us later than
A, set the reference timing to 1 + (-3) us = 0ln -2us.
To adjust the FIFOs to the recommended half full state then the PGM output
will be 13us later than the inputs. Co-timed inputs will then have
approximately half of a HDTV line buffered in their FIFOs. Any sources that
arrive a earlier or later will increase or reduce the FIFO depth respectively.
Set the reference timing to 13 + (-3) us = +10us.
In conclusion, if you know the path delays, set the timing offset to (actual
delay through unit – SDI input timing w.r.t. reference sync timing) in lines
and microseconds.
If the relative delays are not known, use the following:
First, adjust the reference so that the picture is correctly positioned vertically
to the exact line. This can only be done precisely using an HD-SDI data
analyser.
Next, adjust the reference timing to the point at which the output moves up or
down one line. This point needs to be moved away from as it is where the
line FIFO length jumps between 0 and 1 line.
For stable timing move away from this point, for example by half a HDTV
line, to about 13us. Recheck the vertical alignment. If it is out then move the
timing by a number of lines till it is correct.