ZX-News #17 03 декабря 1996

Программирование

Programmers - Catching Reset'a on 128k machines (for example, the game Doble Xinox).

              Programmers



       (C) Michael Blum (Zx-Masters)



   Intercept reset'a on 128k machines.


  Many who play the game "DOUBLE XINOX" and
pressing it to reset, came to the utter dismay, he saw the 
inscription, confirming your decision to drop the program, not

on Scorpion'e, and on ordinary 128!


  To my great surprise, some of these
Many have been some programmers and
Hackers ... The secret of the "glitches" so
simple that I'm just uncomfortable to talk about
him, but at the request of this newspaper, I
do.


  As is known, computer has 128K
two areas of memory reserved for display:
standard - with addresses # 4000_ _ mostly
field memory, and additional - with addresses
_ # C000_ bank RAM7. Select the desired screen should port _ # 
7FFD_, dumping or setting the third bit. If the bit is set, it 
will display a second screen (RAM7), if it is reset, the 
standard (RAM5).



  Now about Reset'e. When the signal arrival
reset is set by hardware standard screen, which clears the 
program initialization, based in turn to address _ # 0000_ in 
ROM at the time of squeezing the button "RESET". 


  Thus, if you use the program only an additional screen in the 
main place any desired message then Reset'e it appears! In 
DOUBLE XINOX'e, for example, the message is in the field 
attributes in order to save memory. 


               === Cut ===


        ORG 30000
START DI

        LD A, 23

        CALL MEMORY

        LD HL, 49152

        CALL CLS

        LD HL, 16384

        CALL CLS

        LD A, 23 8

        CALL MEMORY

        LD HL, TEXT

        LD DE, 22 528 256

        LD BC, 32 * 7

        LDIR
LOOP JR LOOP
MEMORY LD BC, 32765

        OUT (C), A

        RET
CLS LD E, L

        LD D, H

        INC E

        LD BC, 6911

        LD (HL), L

        LDIR

        RET


        ; 12345678901234567890123456789012
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               === Cut ===


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