On-Line #09 05 ноября 1995

Железо

Iron - Why do some programs not working Kempston?

                 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)