Renesas Hitachi H8S/2191, Hardware Manual

Page: 727 / 1065

Rev. 2.0, 11/00, page 700 of 1037
28.7.6 Phase Comparison
The phase comparison circuit takes measures of the difference of time between the reference
signal and the comparing signal with a digital counter. The REF30 signal is used for the
reference signal, and the HSW signal (VideoFF) or HHSW signal (NarrowFF) from the HSW
timing generator is used for the comparing signal. In record mode, however, the phase of the
REF30 signal is the same as that of the vertical sync signal (Vsync) because the reference signal
generator (REF30 generator) is reset by the vertical sync signal (Vsync) in the video signals.
The error detection counter performs the data latching operation at the rising or falling edge of
the HSW signal. The digital filter circuit performs computation using this data as 20-bit phase
error data. After processing and adding the phase error data and the speed error data from the
drum speed control system, the digital filter circuit sends the data as the error data of the drum
system to the PWM modulation circuit.