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28.10
X-Value and Tracking Adjustment Circuit
28.10.1 Overview
To maintain compatibility with other VCRs, an on-chip adjustment circuit adjusts the phase of
the reference signal (internal reference signal (REF30) or external reference signal (EXCAP))
during playback. Because of manufacturing tolerances, the physical distance between the video
head and control head (the X-value:
79.244 mm) may vary from set to set, so when a
tape that was recorded on a different set is played back, the phase of the reference signal may
need to be adjusted. The adjustment can be made by a register setting. The same setting can
adjust the rotational phase of the capstan motor to maintain positional alignment (tracking
alignment) of the video head with the recorded tracks in autotracking, or when tracks that were
recorded with an EP head are traced by a wider head. These tracking adjustments can be made
by acquisition of the envelope signal by the A/D converter.
28.10.2 Block Diagram
The adjustment circuit consists of a 10-bit counter clocked by the servo clock (φs or φs/2), and
two down-counters with load register. Individual setting of X-value adjustment can be made by
the X-value data register (XDR) and tracking adjustment by the TRK data register (TRDR). The
reference signal clears the 10-bit counter and sets the load register value in the down-counter
with two load registers. After the adjusted reference signal is generated, clock supply stops and
the circuit halts until the next reference signal is input. The REF30 signal can be divided (by 2
to 4) as necessary.
Figure 28.37 shows a block diagram.
Rev. 2.0, 11/00, page 718 of 1037
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