VIDEO DISPLAY TIMING ==================== Horizontal line timing ---------------------- * A horizontal line is 64us * HS must be low for at least 4us * DIS must be low for at least 12us * Timing starts from the falling edge of HS This gives the following timing. 00 04 08 12 16 20 24 28 32 36 40 44 48 52 56 60 03 07 11 15 19 23 27 31 35 39 43 47 51 55 59 63 | 4 | 7 | 52 1 | HS| bp | visible f __ ____________________________________________________________ _________ | 4 | 60us | | HS |___| |___| _ ____________________________________________________ __ | 12us | 52us | | DIS |___________| |___________| ________________________________________ : 16us | 40us | 8us : DEN _:_______________| |_______:____________ If we re-arrange things so that the counter starts with DEN, then the horizontal counter is also the memory address counter. This give the following timing. 00 04 08 12 16 20 24 28 32 36 40 44 48 52 56 60 03 07 11 15 19 23 27 31 35 39 43 47 51 55 59 63 __________________________________________________ _________________________ : 48us | 4 | 12us : HS : |___| : _________________________________________________ __________________ : 47us | 12us | 5us: DIS : |___________| : ________________________________________ _____________ | 40us | 8us : 16us | DEN _| |_______:_______________| This allows us to generate the DEN and HS signals directly from the counter: count/4 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 HS ------------------------------------------------XXXX------------ DEN XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX------------------------ Vertical line timing --------------------