Renesas Hitachi H8S/2191, Hardware Manual, Page: 718 / 1065

Rev. 2.0, 11/00, page 691 of 1037
28.6.6 f
H
Correction in Trick Play Mode
In trick play mode, the tape speed changes relative to the video head. This change alters the
horizontal sync signal (f
H
), causing skew. To correct the skew, the drum motor speed must be
shifted to a different speed in each trick play mode, so as to obtain the normal horizontal sync
frequency. To shift the drum motor speed, software should modify the value written in the DFG
preset data register in the speed error detector.
This f
H
correction can be expressed in terms of the basic frequency f
F
of the drum as follows.
N
0
f
F
=
×
f
F0
N
0
+
α
H
(1
−
n)
Legend:
n: Speed multiplier (FWD = positive, REV = negative)
α
H
: H alignment (1.5H in standard mode, 0.75H in 2x mode, and 0.5H in 3x mode for
VHS and
β
systems; 1H for an 8-mm VCR)
N
0
: Standard H numbers within field
f
F0
: Field frequency
NTSC: N
0
= 262.5, f
F0
= 59.94
PAL: N
0
= 312.5, f
F0
= 50.00