Coding - Determining the presence of Kempston Joystick and Kempston Mouse.

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║  Coding.            ║
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(C) EVP-SOFT

            Determining availability of Kempston Joystick.

On the foreign Spectrum Kempston joystick selected by
reset A5 on the address bus, so its port #DF (223), but
on Russian Spectrums with a standard Kempston joystick port
became port #1F(31). In the absence of a Kempston mouse this is not important, and
if any program will access the joystick via #DF
then it will work fine.

   The Kempston joystick bit layout is as follows: D0 - right; D1-
left; D2 - down; D3 - up; D4 - fire, activated bit in
differences from the keyboard is set to 1. In some toys
there is an “inverted” bit layout (for example, in Subway
Vigilante).

   The traditional way to determine the presence of a Kempston joystick
based on the fact that the three most significant bits (D5, D6, D7) if present
reset to 0. For example:


        XOR A
        IN A,(#1F)
        AND #E0  ;#E0 = %11100000
 JR Z, there is a joystick
        No JR joystick


or like this:


        XOR A
        IN A,(#1F)
        R.L.A.
        JR NC, there is a joystick
        No JR joystick


   However, these methods do not work on many Spectrum-compatible devices.
our cars, for example Scorpions, some Pentagons and many
others.  There are several reasons: firstly, on many boards not everything
the most significant bits of the Kempston port of the joystick are reset to 0, it happens that
they are all (or some of them) set to 1; secondly on
branded Spectrums and on Scorpions when contacting any
if there is a missing port, the contents of the port are read from it
attributes ("port #FF")  - this is where the difficulties associated with
connecting a CDOS modem to Scorpion or GRM, because on the board
there is no such port.

   To eliminate the second reason, you need to understand how it works -
no attribute port. Display starts immediately upon arrival
signal INT, more precisely, immediately after INT the upper part is drawn
curb and at this time the attribute port is disabled. When will it start?
the screen begins to draw, then attribute bytes come from the attribute port
ributs that are currently displayed on the monitor (however, in
those moments when the side parts are drawnborder, attribute port
turns off again) - this phenomenon allows you to synchronize the boron
durious effects. So, to determine the presence of a Kempston joystick
(and this also applies to Kempston mice) its port must be polled
only immediately after INT, while the attribute port is disabled, because by-
If there is no joystick, different signals can come from its port.
attribute port trash.

   Well, to eliminate the first cause, it is necessary to determine the presence
Kempston joystick for the least significant 5 bits, but there is truth in this
one drawback, namely, if, when the program checks for the presence
Kempston joystick hold it - the program will not detect
his presence.

 So, the optimal way to determine the Kempston joystick is
works on absolutely all machines with 100% reliability:


;
; (C) EVP-SOFT
;
; while Kempston availability is being determined
; joystick, it is advisable to set the mode
; IM 2 and interrupt routine
; make it short:
;I_ADDR EI
;        RETI
;
TEST_J HALT  ; immediately after HLT the attribute port is turned off.
 XOR A
        IN A,(#1F)
        AND #1F ;#1F = %00011111
        JR Z, there is a joystick
        No JR joystick


 Determining the presence of Kempston Mouse

Mouse name"Kempston" does not mean that it is connected
is installed instead of a Kempston joystick. To connect a Kempston mouse, you need to
wives a special controller, because Kempston mouse coordinates (from -
differences from the AY mouse) are calculated in hardware rather than in software. Communication
with the controller is carried out through three ports:

#FADF - buttons, only the three least significant bits are used, if the bit
        reset to 0, which means the button is pressed: D0-right, D1-left,
        D2-medium.
#FBDF - horizontal coordinates
#FFDF - vertical coordinates

   Mouse coordinates can go through 0 or #FF. Define
the presence of a Kempston mouse is possible by the fact that in its absence from
#FF is read from all three mouse ports, of course, when
The attribute port is turned off. If it came from at least one port
not #FF, it means there is a mouse. However, if after turning on the computer there is no
touch the mouse, then from the coordinate ports will also come
#FF, and the presence of a mouse will not be detected - therefore, after turning on
On your computer, always move the mouse, otherwise no program will
will find. In general, the presence of a Kempston mouse can be determined, for example,
like this:


;
; (C) EVP-SOFT
;
; while Kempston availability is being determined
; mouse preferablyset IM 2 mode
; and the interrupt handling program
; to put it short:
;I_ADDR EI
;        RETI
;
TEST_M LD BC,#FADF
        HALT  ; immediately after HLT the attribute port is turned off.
 IN A,(C)
        CPL
        LD E,A
        INC B
        HALT  ; this HLT can be removed
 IN A,(C)
        CPL
        OR E
        LD E,A
        LD B,#FF
        HALT  ; and it is advisable to leave this HLT
 IN A,(C)
        CPL
        OR E
        JR NZ, there is a mouse
        JR mouse no