An Example of How to Program the Color Palette for 1280 Pixel Resolution and Driving FGBG

In 1280 mode you must use 2 bitplanes to time-multiplex into 1. So, for example, lets use BPO for "early" bytes and BPI for "late" bytes.

7		6		5		4		3		2		1		0		late BP1
7		6		5		4		3		2		1		0		late BP1
7E	7L	6E	6L	5E	5L	4E	4L	3E	3L	2E	2L	1E	1L	0E	0L	final output

The early pixels will be interleaved with the late ones, as shown. So, if you want to alter 1 pixel, you must decide which bitplane it will be in, and operate on its byte.

Make sure the H1280 control bit is set. If it is, BP7 will be forced low for an early pixel, and high for a late pixel. Let's program the palette to multiplex BP0 early and BP1 late and ignore BP2 and BP3. I want my background to be black, and image to be white, and, at the same time have BP3 drive a 640 pixel monochrome screen with the FGBG pin. (it too could be 1280 pixels).