Keyboard error.
(C) Time Keeper / MHCG
Hello, dear users of the greatest computer
of all time - SINCLAIR
ZX Spectrum. (I do not think that
a very loud voice) ...
Today we talk with you, we'll start with one of the most
important devices in any computer of any brand. We
talk about the keyboard ...
After all, on any computer
can not work without a keyboard
since the keyboard is the primary unit of data transmission
by the computer.
It turns out that not all of the Spectrum
so perfect as it might seem at first glance ...
At the Spectrum keyboard is
one very serious drawback.
I call it the "overlap
keyboard. "
Probably many of you began your career on
Spectrum from the fact that for half a day,
and even the whole day, from morning till
late at night playing with toys. Even then, there have been many
entertaining games that cater
for two players. I always liked to sit for an hour the other
together with a friend on the computer and
play Double Dragon, Golden
Axe, etc. But all these games
There is one major flaw: you
probably noticed that sometimes
when playing together, your player just does not listen. For
example, you pressed to the left, and he for no reason,
rhyme or reason suddenly began to jump.
Moreover, such incidents have occurred
most often when the game was played
two players. This is the "overlap of the keyboard."
In the past, like any other
inexperienced user, I thought
This Trouble arises from the fact that programmers improperly
interrogate the keyboard, but I was disappointed when
learn how to program
assembly language and wrote his first
simple program, I discovered
it is still the same damn
glitch ...
At that time I was pretty well versed in circuitry
Spectrum, and finding another scheme Zonovskogo "Leningrad-1, I
began to chase down the cause of this strange phenomenon. It
turned out everything is very simple. Clive
Sinclair in the development of the scheme is stressing the
cheapness the future of the computer and tried to
make it as simple as possible and affordable. It
because of this we are now suffering
and this concerns not only keyboards, but also much more:
inaccurate decoding of internal
ports, because of what is now there are many problems with
connecting additional peripherals You can not boot your own
operating system, impossibility of direct programming
controller ports Floppy disk, a closed architecture ... But
is the theme of individual conversations and
about it, we still raise the question
on the pages of our magazine.
To understand the origins of such
strange behavior of the keyboard,
need to take a closer look at the diagram on your computer. As
known keyboard Spectrum
is a rectangular
matrix size 5 * 8, ie,
it goes five wire data and
eight wires Address:
Q / W /
A10 <- - - -
(K)
A / S /
A9 <- - - -
(K)
Z / X /
A8 <- - - -
(K)
V V
D0 (a) D1 (k)
The figure shows only
part of the keyboard scheme. The remaining buttons are similar.
Assume that the user
by simultaneously pressing
"Q", "W" and "A". Let's see what
happened in reality: How
seen from the keyboard scheme, with
Pressing "Q", closed
Wire A10 (k) and D0 (k) when you press "W", closed
A10 (k) and D1 (k), and finally, when
Pressing "A", closed
A9 (k) and D0 (k) ... Well, what have guessed? When you click
the above Clavey joined: A10 (k) to D0 (a), A9 (k) to D0 (k)
but this means that virtually
united A10 (k) and A9 (k), but
A10 (k) is connected in turn with
D1 (k), then connect the wires D1 (k) and A9 (k), where you can
conclude that automatically
together with the "Q", "W" and "A", pressed
another key and "S"!!! That's it
Behold! And there was no reason to blame all
for programmers to think that
They poll the keyboard correctly. As far as I know the scheme
our domestic computers
they all have a similar defect.
The exception, perhaps, are
computers equipped with IBMklaviaturoy, but I can not exactly
vouch for this since I have
not had a chance to check it.
Of course, this defect is not so
dangerous when operating system software and when you play
alone, but still unpleasant. Ways to solve this problem There
are several, but we consider only one of them:
In my opinion, the easiest way to set the buffer elements in
the each key (at least
I have not found a reasonable solution). You can set the example
five registers K555IR23/K555AP5
on the address bus or on the keyboard
data bus. Or, what seems to me preferable -
purchase IBMklaviatury controller. Connection technology
and the scheme, I will not lead,
as it depends on the particular
example, and consider all the examples, I think, hardly be
since a lot of them. I can not imagine
was to establish buffer elements for each key, I just
just put the two buffers at the ports Sinclair joysticks, since
he I play very little, and the younger
brothers prefer to mostly
joystick ...
