Lprint #09 05 июля 1997

Программирование

Assembler for the user - fill the screen "*".

              Assembler for users (ZX-Spectrum)

(C) Spectre MDM 253-3363

        First published on the Rights of the lessons.


   This column represents a guide for those who mastered the 
spektrumsky Basic and now wishes to explore learn and 
experience the possibilities of language directly control the 
processor. A person fluent in assembler and is not able to use 
it less than perfectly able to write your own programs (games, 
systems, utilities, etc.) for quality to the best works on the 
Spectrum. So, if you dare, and do not mind the phrase "the 
assembler is very difficult to teach," then read on, otherwise 
just go to the following article. 

   To get started you will need some assembly. Their choice
is large enough (XAS, PASM, TASM, MASM, ALASM, ZASM), but I 
suggest to stop immeno ZASM'e. If you have a modem, then I I 
think you will quickly persuade anyone to give you ZASM'a, but 
if no (modem), then look at their system disks - can ZASM 3.0 
somewhere, and lying. Suppose your quest to succeed, and you're 
not too lazy to read the following instructions to ZASM'u, then 
you can start. 

   To begin with we write the procedure, the action that you 
immediately see on the screen:



        ORG 30000

        LD HL, 42 * 8 15 616

        LD DE, 16384

        LD B, 8
METKA LD A, (HL)

        LD (DE), A

        INC HL

        INC D

        DJNZ METKA

        RET


   Now, comments:

  - Commando ORG need to know assembler, according to kako
    Therefore, the address will be your program.

  - Number of character "*" (star) = 42. One character takes a

    8 bytes of memory, and memory with the symbols begins at 
address 

    15616. Means for calculating the address where the 
information     tion of our sprocket, we believe: 42 * 8 is how 
many bytes 

    skip from the beginning, plus 15616.

  - 16384 (# 4000) is the address of the start screen

  - LD B, 8 how many bytes needed to display

  - LD A, (HL) take a byte from the address addressable HL

  - LD (DE), A put the address in DE

  - Increase the address of the HL 1

  - Increase the address in DE 256 (due to the linearity of the 
screen) 

  - Using command DJNZ program loops 8 times (it

    we asked in B)

  - RET return to the assembler.


   At present, while all but if you need this topic, I'm her
must go on, just throw at least one message on
any Minsk bbs, or call me (call Andrew).