Vertical Sync Signal Threshold Register (Vvthr) - Hitachi H8S/2199 Hardware Manual

Single-chip microcomputer

Table of Contents

Digital H separation

H complement and

mask counter

When Complementary Pulses Inserted Three Successive Times While HHKON = 1

Vertical Sync Signal Threshold Register (VVTHR)

Initial value :

The VVTHR is an 8-bit write-only register for specifying the threshold value for the digital V

separation counter; this value is used to generate the SEPV signal from the Csync signal. The

SEPV signal is set to 1 when the digital V separation counter value matches the VVTHR value

while the Csync is high, and reset to 0 when the digital V separation counter value becomes 00

while the Csync is low. Set the VVTHR value so that the SEPV signal goes high 1/2H or more

after the Vsync start point. When reset, the VVTHR is initialized to H'E0.

Figure 27.8 shows the VVTHR value and the SEPV signal generation timing.

Digital V separation

Figure 27.8 VVTHR Value and SEPV Generation Timing

Forcible HHK

Figure 27.7 Timing of HHK Operation

1/2 H or more

Forcible HHK

Rev. 1.0, 02/00, page 773 of 1141