Splitting the Atom

page 52

Graphics mode 1

In this mode the VDU display is mapped from 1024 bytes (1K) in the format 16 across and 64 cells down.

8000		800F	64 rows of cells = 64 pixels
83F0		83FF
	16 columns of cells = 128 pixels

Each graphics cell has eight pixels which correspond to the eight bits in a byte (labelled 7 to 0)

7	6	5	4	3	2	1	0	Bit label number
One graphics cell

When the bit is set the pixel is white, when the bit is clear the pixel is black. Thus:

Cell shade								Binary	Hex
								1000 0000	80
								1100 0000	C0
								1110 0000	E0
								1111 0000	F0
								1111 1000	F8
								1111 1100	FC
								1111 1110	FE
								1111 1111	FF

Graphics mode 2

The display is mapped from 1536 bytes (1.5K) with 16 cells across and 96 cells down.

8000		800F	96 rows of cells = 96 pixels
85F0		85FF
	16 columns of cells = 128 pixels

The arrangement of the graphics cell is the same as for mode 1.