Rev. 1.0, 02/00, page 656 of 1141
26.10
X-Value and Tracking Adjustment Circuit
26.10.1
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 the acquisition of the envelope signal by
the A/D converter.
26.10.2
Block Diagram
The adjustment circuit consists of a 10-bit counter clocked by the system clock (
φ
s or
φ
s/2), and
two down-counters with load registers. Individual setting of X-value adjustment can be made by
X-value data register (XDR) and tracking adjustment by 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. REF30 signal can be divided as necessary.
Figure 26.37 shows a block diagram.