Spectrofon #16 20 декабря 1995

Программирование

System - about compatibility issues with Spectrum clones. Programming Fundamentals musical processor AY-8910/12.

           SYSTEM


  Potekhin Leonid

    LeoSOFTWARE from * SA *


   I would like to continue the theme of
compatible computers. First, a bit of known software reception 
OUT (# FD), A. This reception is used in two cases: for 
switching pages of RAM (Port # 7FFD) and to refer to

music coprocessor (port
# FFFD). According to my research, he
fails to SCORPION'ah,
ATM machines, some 128K collected either on a single large chip 
or on a former 48K machines memory which expanded to

128k.



   The main purpose of
this technique - save a little on the speed and free register 
under the Sun for other purposes. List of non-business programs 
is large enough, a lot corrected. But the worst thing that

in spite of all, many programmers continue to produce programs 
with a similar flaw. Switch pages through port

# FD is still possible (as - more on that below), but apply to 
a musical coprocessor probably still is the port # FFFD. 


   The idea of ​​using the port # FD
to turn the page of RAM is that the above listed computers 
through the port # FD page RAM correctly switch, change the 
active screens, but this requires

in a byte that is sent to
port, install the sixth bit
ie:

to switch to bank 0 of RAM in the
Port will travel byte # 50

to switch to a bank of RAM in the
Port will travel byte # 51

to switch to the bank RAM 2 in
Port will travel byte # 52

to switch to 3 bank RAM in
Port will travel byte # 53

etc.


   It is possible that similar
focus can not go on the computers where the sixth bit port
# 7FFD used in some
purposes. (By the way, I would like to know what kind of car. 
The program CONVER COMMANDER v3.02 there is a similar treatment 
seems to change pages). For versatility

can offer a simple way
Recognition of different computers:

Text of the program switching
page looks like this:

ADR1 LD A, # 11

        OUT (# FD), A

Similarly, suppose somewhere further
meets the same piece of code labeled ADR2. In the beginning
The program should be done about this procedure:
(Of course, it should be located in memory address above
# C000)



DI
LD BC, # 7FFD
LD DE, # 1011
LD A, (# FFFF)
LD L, A
INC A
LD (# FFFF), A; RAM 0, (# FFFF)  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 - the addresses to which you can access, avoiding 
conflicts on the data bus. It is easy to see that all addresses 
discharge A5 is 0. That principle

rough deciphering this category
"Responsible" for KEMPSTON JOYSTICK.
That is, the values ​​of the joystick theoretically be read by
all of these addresses.


   In fact, anyone KEMPSTON
JOYSTICK performed on m / scheme
KR580VV55, the values ​​of the joystick
will only be read at
# 1F (31). That is why, in some programs where there is a poll 
on the mask # DF, the joystick will not work. Problem Solving 
seems to replace 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 everyone who cares
Questions of iron, and who has
own findings can call me on my ZX, repeat,
namely ZX BBS.



   Desirable to issue his findings in a file in the ZX-WORD, and
put me on the server. This is the case, however, only residents
Moscow and the region. Others can write to me.


   I express my great appreciation to:

 MIKHAIL Khokhlova (company "Condor") for the great help
in my work.

 DENIS LEZHENKO (LDESoft) for the solidarity and the original 
technical findings. 

 ALEKESEYU and all FFC for your cooperation.

 "Inforkom" in their right over it.

 "SPECTROFON" and STEP CREATIVE GROUP for a beautiful and
useful journal.

 "ONLINE" and Grigoryev DMITRY (OLDMAN) for efficiency and 
competence. 

   My address is: Moscow, Guryevsky Ave respect, Building 19,
Building 2, Apt. 311.


   Phone: 397-65-08


   Call from 20.00 to 22.00.


   CS BBS runs on Wednesdays, Thursdays and Fridays from 01.00 
to 06.00. 


         Kirill Gromov (C) CHUNG

                  Software (FFC)