Vertical resolution of the 7800

[DracIsBack]

I was having a discussion with another classic gamer on resolution of various systems and it became clear that I'm not quite sure what the 7800's vertical resolution actually is.

 

I know games are either 160 or 320 pixels wide, but how many pixels vertically?

 

I know computers often have a fixed vertical resolution like 320 x 240, 320 x 192 etc, but what about the 7800?

 

I've heard it's vertical resolution is either 192, 200 or 240 pixels. Or does MARIA draw as many scanlines as she needs up to a point?

Edited February 23, 2018 by DracIsBack

[Mord]

Atari's recommended resolution was 192 back in the day to make sure the entire visible screen is actually visible on most TVs back in the 80s. But the 7800's DMA can do more. In 7800Basic you can specify up to 224. Not sure if it can do even more than that or not, as the DMA stops on scanline 240 (but doesn't actually start on line 0 of a tv frame iirc).

 

The problem with going over 192 is that it means there's less time for the 7800 to do game logic, etc. Essentially it's up to the programmer to decide if they want the vertical resolution to be 192, 208, 0r 224, etc.

Edited February 23, 2018 by Mord

[Trebor]

Some examples are provided in this post. It includes a comparison picture. For instance, the original retail games Water Ski and Tank Command both utilize 224 lines. Ballblazer appears to be around the 208 marker and Ms. Pac-Man at the 192 spot.

 

A game could display up to 240 lines, but in harmony with what Mord posted above regarding the entire screen being visible, on average, a CRT cuts off ~8 lines from the top and bottom...240-16=224.

[DracIsBack]

Thanks for clarity!

[Fragmare]

Yea, what they said... almost all these old 8-bit (and 16-bit) consoles used a maximum displayable area of 240 scanlines, but most TVs around at the time only displayed between 200 and 220 (I had an old Toshiba that did 230-ish, though). So most game developers used something less than 240, like 192 or 224... this had another advantage besides ensuring all the graphics are visible... any undrawn scanlines can be devoted to more CPU time during vblank... which means more complex code can be used, and in turn, more complex game logic, object behavior, etc.

[Trebor]

This thread reminded me of one started by Thomas Jentzsch. There's a 2600 test program provided which can be utilized by any curious in measuring the number of vertical lines shown by their display.

Sure enough, the majority (60%) of the NTSC CRT tested average to just sightly over 224 vertical lines (224.2):

NTSC:    100%, 28 tests    | 60%, 21 tests
Average: 26.7, 217.8, 17.9 | 23.3, 224.2, 14.5
Min:     19  , 190  ,  8   | 16  , 215  ,  6
Max:     41  , 234  , 31   | 30  , 239  , 22 

PAL:     100%, 19 tests    | 60%, 14 tests
Average: 31.4, 263.1, 18.1 | 29.1, 269.1, 14.5
Min:     24  , 234  ,  7   | 21  , 255,    7 
Max:     37  , 280  , 42   | 36  , 283,   24

[Fragmare]

Yea, and that's just an average. It's understandable that Atari would recommend 192 scanlines, since some REALLY old TVs didn't do anywhere close to 240, and there were still a lot of REALLY old TVs in use at that time. Ever see those old flat-ish Sony Trinitrons or Toshiba TVs? They could do a good 230, maybe even more

[Trebor]

... Ever see those old flat-ish Sony Trinitrons or Toshiba TVs? They could do a good 230, maybe even more

I was quite surprised at the entries for NTSC CRT TVs that provide 234 and even 239 lines!

[DracIsBack]

Yea, and that's just an average. It's understandable that Atari would recommend 192 scanlines, since some REALLY old TVs didn't do anywhere close to 240, and there were still a lot of REALLY old TVs in use at that time. Ever see those old flat-ish Sony Trinitrons or Toshiba TVs? They could do a good 230, maybe even more

 

One of those Toshibas displays my 8bit consoles to this day! :-)