IRON
AND AGAIN ON COMPATIBILITY
I recently often asked: "Why do we have some programs not
working KEMPSTON JOYSTICK?". Reasons here a few, and I hasten
their will explain. To do this, dip a little in circuitry of
our beloved SPECCY.
The first, initially in his native SPECCY all ports decode
roughly, one category lower byte data bus. This will be
clear from the following table:
Port # FF 11111111 O-O-O-H, MY GOD!
Port # FE 11111110 BORD, MAG, BEEPER, KEYB
Port # FD 11111101! READ BELOW!
Port # FB 11111011 ZX-PRINTER
Port # FF actually read, not only in its historical address,
and in general for any unused. Port # FD in fact, can not be
used directly as possible "Answer" multiple devices - the port
configuration ZX 128, muz.soprotsessor. Although it is often
used to switch the memory pages. On the computer where it is
implemented as a corporate SPECCY, these numbers are. But on
the hill-computers such as "ATM" and so on (you understand me),
this leads to sad results.
These were the main ports, now on.
Port # F7 11110111 \
Port # EF 11101111} ZX LPRINT 3
Port # E7 11100111 /
As you can see, still addresses # 1F to # DF. In binary form
this looks like this:
Port # 1F 00011111
Port # 3F 01011111
Port # 9F 10011111
Port # DF 11011111
This is the address for which you can access, avoiding
conflicts data bus. It is easy to see that all addresses
discharge A5 is 0. That is the principle of brute decryption of
this category of "responsible" for KEMPSTON JOYSTICK. That is,
the values of the joystick theoretically be read by all those
addresses. In fact, anyone KEMPSTON JOYSTICK performed on m /
KR580VV55 scheme, the values of the joystick will be read
only at # 1F (31). That is why, in some programs where there is
a poll on the mask # DF, joystick will not work. Solving the
problem seems to be replaced on the mask # 1F. Indeed, why make
unnecessary extra logic and torment the computer when the
address # 1F has become a de facto standard in our country. I
think that gave an exhaustive answer to this question.
In conclusion, I want to say that all who are not indifferent
Questions of iron, and who have their own discoveries, can call
me on my ZX, I repeat, it was ZX, and not the PC (stinking
machine), BBS. Desirable to issue his findings in a file in the
ZX WORD and put me on the server. This is the case, but only
residents of Moscow and the region. Others can write to me.
Kirill Gromov (C) CHUNG Software (FFC)
