* PSET seems to use an internal x and y coordinate.
* The internal x and y coordinates are validated before use by masking them. When width is 256 then mask is 0x0ff, when 512 the mask is 0x01ff, when 1024 the mask is 0x03ff and when 2048 the mask is 0x07ff. Therefore attempting to write to x=300 on a 256 width screen actually writes to pixel x=0x02c.
* During testing I found that the 'advance' part of the PSET command differs slightly from the official document.
- The document claims that when AXE and AXM bits of the command are 0 then both DX and DY registers are read and the internal x and y are updated. I didn't find this. I found that when AXE and AXM are 0 then only the DX register is read and the internal x coordinate is updated from it. DY is not read at this time. Testing also shows this happens at the start of PSET command execution.
- If DY register is written the internal y coordinate is updated immediately. Writing to both register 38 and 39 update the internal y coordinate.
- The internal X and Y coordinates are incremented or decremented based on AXE, AXM, AYE and AYM. The internal x and y will wrap within the width and height of the display. The width is wrapped using masking. e.g. When the screen is 256 pixels wide, x is 0 and is decremented it will wrap to 255 and if x is 255 and is incremented it will wrap to 0. The same is true of the Y coordinate.
* With the command engine, tested on PSET currently (but to be confirmed for other commands):