Product specifications

The graphics pattern display colours can be any two of 16 (including

transparent) sectioned into groups of 8 characters.

The backdrop or border colour can be any one of 16 (including

transparent).

The character patterns can be dynamically changed to give any number

of character patterns limited by the amount of storage space in Z80 RAM

for the extra pattern libraries.

Sprites are available up to a maximum of 32.

The VDP is in Graphics 1 mode, when mode bits M1 = 0, M2 = 0 and M3 = 0 (see

section 2.2 register 1 bits 3 and 4).

One of the major advantages of this mode is that it is very compact, requiring a

maximum 2848 VRAM bytes for a complete set-up. Yet it is possible with some care

to create graphics effects very similar to those available in graphics 2 mode.

Like text mode, it is also possible to build up several different pattern libraries in

VRAM and several screens, and switch to a complete new graphics 1 mode set-up by

changing only two VDP write-only registers.

And again like text mode it is possible to have one pattern library held in the pattern

generator table, and to have up to 14 completely separate display screens, which can

be changed to a new screen by changing only one VDP write-only reg A,E ;Get data

byte

OUT (2),A ;Output data byte

LD A,D :Get control byte

AND 7 ;Set up correct control bits

OR 128 ;Set bits 6,0w

VRAMsub-block Length in bytes

Pattern generator table 2048

Pattern colour table 32

Pattern name table 768

The pattern generator table is 2048 bytes long and is split into 256 graphics patterns,

each of which is 8 bytes long.

Each block of eight bytes in the pattern generator library define a graphics pattern in

which the 1’s take on the foreground colour assigned to its, while the 0’s take on the

appropriate background (or backdrop) colour.

These colours are chosen by loading the correct byte of the pattern colour table with

the appropriate colour byte in a very similar way to that used to load VDP register 7 as

described in section 2.2 example 1.

The difference is that these colour control bytes are held in VRAM and do not need a

routines described in section 1.