Product specifications

M1 M2 M3

0 0 0 Graphic 1 mode

0 0 1 Graphic 2 mode

0 1 0 Multicolour mode

1 0 0 Text mode

Bit 2 Reserved and must be zero.

Bit 1 SIZE selects Sprite Size

1 selects size 1 sprites (16 times 16 bits).

0 selects size 0 sprites (8 times 8 bits).

Bit 0 MAG is the magnification option for sprites.

1 selects MAG1 sprites (SIZE times 2).

0 selects MAG0 sprites (SIZE times 1).

table sub block, in other words, the start address of the VRAM display

screen.

It is a four bit value and therefore has a range of 0 to 15, which it must

not exceed. Bits 7,6,5 and 4 of this register must be zero.

The name table must be located on a 1k boundary, so if we were to load

this register with say 7, the VRAM display screen would start at 7K or

£1C00 Hex. If we loaded it with 15, the VRAM display screen would start

at 15K or £3C00 Hex. In text mode this table is 960 (24 times 40) bytes

long.

In all other modes this table is 768 (24 times 32) bytes long.

sub block. This holds the colours of the patterns used in graphic modes

1 and 2. It is not used by text or multicolour mode. Text and multicolour

mode are covered in sections 2.5 and 2.7 respectively.

Graphic modes 1 and 2 access the colour table in different ways. This

means that the set up bits for this register are different dependant on

which graphic mode you wish to use.

In graphic one mode the colour table is located on a 64 byte boundary

and is 32 bytes long. If we wanted to locate it at 8k (£2000 Hex), we

need to divide 8k (3192 Decimal) by 64, and then load the result into

For a fuller description of how graphic mode 1 works see section 2.6.

In graphic two mode, which is the usual BASIC graphic mode, the colour

table is located on an 8k boundary. As the VDP uses 16K of VRAM, this

means that the colour table can be located at either address 0K or 8k

only.