5
Function
Timing and Control
The Microcontroller interfaces between front panel controls and
the crosspoints and registers of the Digital Matrix and Blanking
Gate Limiter and Rounder circuits. The controller also configures
the chroma channel low pass filter ASICs and feeds registers
which determine the mix coefficients for the Digital Matrix.
The external and internal (G/Y) reference inputs are amplified
and then fed to a selector. The selected reference is low pass
filtered to remove burst (if the reference was color black) and fed
to a Sync Separator.
The Sync Separator extracts sync from the selected reference. A
Lock Phase Error Detector compares Local Horizontal Timing
with separated sync to create a phase error voltage.
Separated reference sync (Sync) also feeds a Reference Vertical
Detector which generates a reference vertical pulse (Ref Vertical)
to the Ref Sync Presence Detector and the Vert(ical) Timing
Generator and Auto Standard Logic circuit blocks.
The 27MHz VCXO generates the master clock for the video A/D
converters. The Horizontal Timing Generator generates a
horizontal rate square wave which drives the previously
mentioned Lock Phase Error Detector to create a phase error
voltage (Freq Control) which controls the 27MHz VCXO. The
resulting phase-locked-loop locks the Horizontal Timing
Generator outputs and the clocks to the reference video
horizontal.
The Vertical Timing Generator receives a 2H clock and uses it to
create vertical frequency outputs. The Ref Vertical input is used to
set the phase of internal counters to phase the vertical blanking
and field outputs to the vertical reference. The circuit also
provides automatic 525/625 standard selection by comparing Ref
Vertical and internally generated timing pulses.
347301A1.book Page 5 Thursday, November 2, 2000 10:41 AM
