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I'm thinking of doing a project in MSX BASIC. I've seen some books where they discourage setting the width of SCREEN 0 to 40 characters wide with the WIDTH command (or 32 characters wide in SCREEN 1), since it would go beyond what the televisions of the time were able to display.

I don't have a real machine, and it's a non-issue with emulators.

Is this a problem on real hardware?

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    I would think that the higher resolutions would be more likely to not work with old televisions.
    – paxdiablo
    Mar 8, 2023 at 11:06
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    @paxdiablo the MSX had composite video output. this question isn't about resolution.
    – Sneftel
    Mar 8, 2023 at 13:12
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    Mind to add sources for that claim?
    – Raffzahn
    Mar 8, 2023 at 14:21
  • I also think it isn't true that "the MSX had composite video output". Many MSXs did, some didn't. But that's really pedantic stuff. It's going to be composite or better.
    – Tommy
    Mar 8, 2023 at 15:59
  • @Sneftel MSX is not one certain computer, but many companies produced many different MSX computers. Many MSX computers had RF outputs and as far as I understand correctly, the manufacturers need not neccessarily add another video connector but the RF connector was enough. Mar 9, 2023 at 12:17

1 Answer 1

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At width=40, 240 pixels are generated from a nominal line width of 342; subtracting the 58/342ths of the line that is used for blanking and sync that means around 84% of each line is pixels. Using all 32 columns in one of the other modes would be slightly wider at 256 pixels for almost 90% coverage.*

The classic title-safe area per SMPTE RP 8 is the central 80% and the classic action-safe area is 90%** — i.e. it is recommended that if a TV programme puts text on screen then it shouldn't be outside of the central 80% of the screen in order to ensure that all viewers can read it, but important action can occur anywhere in the central 90%.

So it is indeed a risk to use all 40 columns and require that the user be able to read them all.

The MSX 2 adds the hardware ability to shift the entire display up to 8 pixels in any direction relative to the frame, to ameliorate.

Such as it may help for comparison, the ZX Spectrum 128k's 256 pixels are compressed into 128/228ths of the line compared to the MSX's 256/342ths, i.e. the MSX's display is about a third wider; similarly it's coming up on 20% wider than the full width of an Acorn or Amstrad CPC. The Master System has exactly*** the same pixel timing as the MSX so the risk is situations like this one where the right-hand side of the game has been cropped by the TV.

* Check out this in-depth look at TMS9918 and V9938 timing, zoom in on the diagram and observe from the TMS rows at the bottom: (i) that there are 342 clocks total per line; (ii) that the synchronisation pulse runs in the left during what the author has numbered clocks 0 to 26, followed by a left erase signal (i.e. blank and colour burst) up to clock 50 and the right erase time begins at clock 334, for 342-334+26 = 58 clocks on the part of the line without visual content.

** I can't find the primary source online; here's one of many secondary references.

*** other than that any game that scrolls horizontally probably disables the first column for a 31-column display, including Sonic as depicted.

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