ZX Computings - OpenLibra

are on screen at a time.
Although this is not the bestlooking
Defender for the ZX81
on the market, it plays
remarkably well, and is greatly
enhanced when the sound
board is connected.
QS Asteroids, which needs
a ZX81 or New ROM ZX80
with the SLOW modification, is
a pretty good version of the arcade
game, despite the oddlooking
asteroids. Quicksilva
had 'intelligent' asteroids
which homed in on your ship in
an early version but discovered
that such a game was impossible
to defeat, so the program
you'll get now is a faithful copy
of the arcade game,
QS Invaders is the biggest of
Quicksilva's games, with a full
7K of machine code (plus a little
BASIC). There are seven rows
of 13 invaders. To see this program
running with userprogrammed
invaders on the
character board, with sound, is
to imagine you're watching a
proper arcade machine in action,
despite the lack of colour.
A number of manufacturers
have produced invader programs.
This one, without the
sound and user-programmed
characters, is pretty much par
for the course.
The Sound Board
The sound chip used in the
board has 1 6 internal registers,
each of which control a different
section of the sound
generation. Registers 0 and 1
are for controlling the tone and
pitch of sound channel A,
registers 2 and 3 control channel
B and 4 and 5 the channel C
tone source. Register 6 tunes
the noise generator and register
7 is used to switch the various
sound sources, controls the
switching of the tone generators,
the switching of the two
ports to input or output.
Registers 8, 9 and 10 control
the volume of each channel, 11
and 12 set the length of one
envelope cycle and register 1 3
controls the envelope shape
and pattern. A number of sample
routines have been provided
by Quicksilva showing how
flexible and useful the sound
board can be. Music, explosions,
trains and phasers can all
enliven programs.
Character
Generator
This is a single circuit board
which plugs directly into the QS
Motherboard, or via the QS
connector directly into the
computer. There are 128 fully
programmable characters, and
the board can be used with existing
software. A lower-case
alphabet is provided as part of
the character generator demonstration.
The OS Motherboard
Some kind of motherboard is required
if you want to hook more
Hardware support
than just the printer and a RAM
pack onto the ZX81. The QS
Motherboard at £ 1 2 represents
a very cheap and useful addition
to your system. The
motherboard is fitted with its
own 5 V regulator to drive all
external boards. There are two
expansion sockets on the
motherboard.
/
M M
wmi
Quicksilva are at 95 Upper
Brownhill Road, Maybush,
Southampton, Hants.
Part of the impressive range
of hardware support provided
by Nick Lambert's company,
Quicksilva.
76 ZX COMPUTING SUMMER 1982