SC-3000X uses the Altera DE1 VGA output driving almost any LCD screen/display.
VGA Settings
Screen resolution: 640 x 480 pixels x 59,6374 Hz
Field resolution: 800 x 524 (640 x 480 viewable area)
Low-res resolution: 400 x 262 (320 x 240 viewable area)
Color depth: 12bit/4096 colors (4 red, 4 green, 4 blue)
Hi-res (640x480) pixel clock: 25 MHz
Mid-res (640x240) pixel clock: 12,5 MHz
Low-res (320x240) pixel clock: 6,25 MHz
VGA system runs everytime at 640x480 doublin the rows and columns for low-res (320x240) and doubling ONLY the rows for mid-res (640x240).
VGA draws pixel data into a line buffer of 320 pixels repeating every pixel two times for lowres in order to fill 640 width viewable area. For midres pixel are got as is.
Meanwhile VDP build new data (288/576 pixel) into internal buffer line.
On the end of even rows VGA signals emulated VDP to restart HBlank so VDP are everytime in synchro with VGA and the TWO buffer lines are swapped.
VDP draws starting from pixel n. 32 (hires) or 16 (lowres) so we have two black bands surrouning 288 width screen image filling so the 320 viewable area (16 + 288 + 16).
VGA lowres pixel clock is 6,25 MHz allowing 400 pixel total and 320 pixel active area for every row and
VDP lowres pixel clock is 5,3571 MHz allowing 342 pixel total (342,857142 truncated by hblank) and 288 pixel active area.
Horizontal dots: 800 pixels
Line frequency: 31250 Hz (25.000.000 / 800)
Line period: 32 us (1.000.000 / 31250)
Horizontal visible area dots: 640 pixels (25,6 us)
--- VERTICAL SETTINGS -----------------------------------------------------------
Vertical rows: 524 rows
Vertical visible area: 480 rows
Field frequency: 59,6374 Hz
Original SEGA SC-3000 Video Settings
Screen resolution: 256 x 192 pixels + border
Field resolution: 342 x 262 (NTSC 60Hz)
Field resolution: 342 x 313 (PAL 50Hz)
Pixel clock: 5.369317 MHz
Horizontal dots: 342 pixels
Line frequency: 15699,7573 Hz (5.369.317 / 342)
Line period: 63,6952 us (1.000.000 / 15699,7573)
Horizontal visible area dots: 284 pixels (52,893 us)
HORIZ. VIEWABLE AREA (284 pixels):
Left border: 13 pixels (19 pixels TEXT MODE)
Active area: 256 pixels (240 pixels TEXT MODE)
Right border: 15 pixels (25 pixels TEXT MODE)
HORIZ. HIDDEN AREA (58 pixels):
Right blanking: 8 pixels
Horizontal sync: 26 pixels
Left blanking: 2 pixels
Color burst: 14 pixels
Left blanking: 8 pixels
--- VERTICAL SETTINGS -----------------------------------------------------------
VERT. VIEWABLE AREA - NTSC (243 rows):
Top border: 27 rows
Active horizontal area: 192 rows
Bottom border: 24 rows
VERT. HIDDEN AREA - NTSC (19 rows):
Bottom blanking: 3 rows
Vertical sync: 3 rows
Top blanking: 13 rows
SC-3000X Video Settings
Screen resolution: 256 x 192, 512 x 192 pixels + border
Field resolution: 800 x 524 (VGA 59,6374 Hz)
Pixel clock: 5,3571 MHz
Horizontal dots: 342,857142 pixels (horizontal sync from VGA cut pixels to 342 as original SC-3000)
Line frequency: 15625 Hz (5,3571 / 342,857142)
Line period: 64 us (1.000.000 / 15.625)
Horizontal visible area dots: 288 pixels (53,76 us)
HORIZ. VIEWABLE AREA LOWRES (320 pixels):
Left BLACK border: 16 pixels
----- [START] EMULATED AREA (288 pixels)
Left border: 16 pixels (24 pixels TEXT MODE)
Active area: 256 pixels (240 pixels TEXT MODE)
Right border: 16 pixels (24 pixels TEXT MODE)
----- [END] EMULATED AREA (288 pixels)
Right BLACK border: 16 pixels
HORIZ. HIDDEN AREA LOWRES (80 pixels):
--- VERTICAL SETTINGS -----------------------------------------------------------
VERT. VIEWABLE AREA LOWRES (240 rows):
Top border: 24 rows
Active horizontal area: 192 rows
Bottom border: 24 rows
VERT. HIDDEN AREA LOWRES (22 rows):