CRTC comprehension: are the BASIC display modes lopsided?

[ThomH]

Per the wiki's entry on the CRTC:

When HSYNC is active Gate-Array outputs the palette colour black. If the HSYNC is set to 14 characters then black will be output for 14us.

It also provides BASIC's selections for various CRTC registers, specifically:

   
• horizontal total = 63
• horizontal displayed = 40
• horizontal sync width = 14
• horizontal sync position = 46

So to me that suggests:

   
• there are 64 columns per line (numbered 0 to 63);
• of those, columns 0 to 39 are pixel content;
• sync starts at position 46 so there are six columns of border on the right: columns 40, 41, 42, 43, 44 and 45;
• sync lasts for 14 columns so it ends just before column 60, having lasted from 46 to 59 inclusive;
• there are then four columns of border on the left: columns 60, 61, 62 and 63.

Therefore there are six columns of border on the right but only four on the left.

Is my understanding correct? Is 48 columns the maximum width that an appropriately-calibrated monitor can show while keeping BASIC centred?

[Longshot]

Yes your understanding is correct.
About 48 : On a CTM monitor probably, but not on other monitors.
50 is probably the best way to no longer have a border on any monitor.

[ThomH]

Yes your understanding is correct.
About 48 : On a CTM monitor probably, but not on other monitors.
50 is probably the best way to no longer have a border on any monitor.

That surprises me, because but if it's what the numbers mean then so be it.

Mapping that to the other dimension, I had a quick run through CPC games that are in my memory as being 'tall' and the tallest I could find was Donkey Kong at 256 lines. Mathematically I think it should just barely fit if you assume a vertical retrace period at the slightly speedier end of the usual range — or, with the same outcome, if horizontal and vertical sizes are calibrated very slightly differently.

So I guess the largest display that would make sense for a CTM is 48 columns by 256 lines. And, as you say, for other monitors maybe a shade larger than that.