Basic Programming Question

[tmop69]

16 minutes ago, Lee Stewart said:

 

 

Effectively, you have only a 5x7 matrix for characters in Text mode because you want a 1-pixel character separation for both columns and rows. Though you can certainly define characters to fill the 6x8 matrix, they will run together if you do. Though you lose the rightmost 2 pixels of each character, you must define each character as an 8x8 matrix in the character pattern table.

 

And, indeed, the effective screen is only 240 pixels wide and, I would guess (others will know better than I), centered with an unavailable 8-pixel border on each side.

 

...lee

Yes, it seems correct the two 8pixels borders.

See https://github.com/cbmeeks/TMS9918/blob/master/tms9918a.txt at chapter 3.2

 

[apersson850]

21 hours ago, Lee Stewart said:

Effectively, you have only a 5x7 matrix for characters in Text mode because you want a 1-pixel character separation for both columns and rows.

I use a 5*8 matrix for the character definitions, since I want true descenders on some letters. The do meet the top of high letters on the row below, but I've found the end result is still better that way.

To avoid confusion, the VDP chip is a TMS 9918A in NTSC consoles, or TMS 9929A in PAL consoles for 50 Hz. Rich mentioned the TMS 9901, but that's the PSI (Programmable System Interface), which provides inputs, outputs and a timer.

 

The p-system also uses 40 columns as the standard screen, sideways buffered to offer 80 columns. Similar to what Editor/Assembler and TI Writer does. The p-system also supports the 32 column and multicolor modes, but just switching to them. As I've demonstrated, the p-system can be convinced to support bit-mapped graphics too. In that mode you have full control of 256 by 192 pixels.