Info Guide #01

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Programming - A few short and fast procedures.

                 Etudes
  Alone Coder


   In this section we will publish short and quick procedure 
that we recommend to use instead of the ancient and 
gromozdkih.Takzhe will include small changes in the old 
procedures, which give some advantage over the latter.



   Change in the seemingly already classical procedure DOWN HL, 
which is known to expects a byte address on the screen, lying 
on a pixel is below this in the HL: 

      Was: It was:

     INC H INC H

     LD A, H LD A, H

     AND 7 AND 7

     JR NZ, EXIT JR NZ, EXIT; CY = 0

     LD A, L LD A, L

     ADD A, 32 ADD A, 32

     LD L, A LD L, A

     JR C, EXIT JR C, EXIT; CY = 1

     LD A, H LD A, H

     8 SUB ADD A, -8

     LD H, A LD H, A; CY = 1
EXIT ... EXIT ...

   In this version everything was still, except that the flag 
CY is now points to the current border crossing

familiarity. In the procedure UP HL can produce a similar 
change: instead of ADD A, 8 put SUB -8.



   : the coordinates specified by
in the registers L = y, E = x, in any place
screen (and even off the screen) over 58 (!) cycles put 
tochka.Registr C is the high byte address table ('TABLE), the 
register D = C +2. 

     LD H, C

     LD A, (DE); x / 8

     INC D gives the least significant byte

     OR (HL); L (y)

     INC H

     LD H, (HL); H (y)

     LD L, A

     LD A, (DE); byte (x)

    (X) OR (HL); method of staging points

     LD (HL), A

   If, instead of the last 2 Paste
AND (HL), it will feature POINT. To
procedure has worked many times at the end of its
Put DEC D. Tables are generated the following program:

     LD HL, TABLE +256

     LD DE, # 4000
GEN0 LD (HL), D

     DEC H

     LD (HL), E

     INC H

     DOWN DE 1-I

     LD A, D and

     SUB 88 2-I

     JR NZ, $ +3

     LD D, A

     INC L

     JR NZ, GEN0

     INC H

     LD A, 128
GEN1 LD (HL), E

     INC H

     LD (HL), A

     DEC H 3rd

     RRCA and

     JR NC, $ +3 4-I

     INC E

     INC L

     JR NZ, GEN1


   Fragment program, which allows for some
and the same 19 bars of yes / no
semitaktovuyu command (Z - perform, NZ -
not to perform):

     JR NZ, $ +4

     JR EXIT

     
EXIT ...


   Fast print letters 6x8 (screen DE):

     PUSH DE

     LD L, A

     LD B, C

     LD A, 2

     RRCA

     DJNZ $ -1

     LD (PRN +1), A

     LD H, 'FONT

     LD B, 8
PRGO PUSH HL

     LD L, (HL)
PRN LD H, 1
PR1 ADD HL, HL

     ADD HL, HL

     JR NC, PR1

     LD A, (DE)

     OR H

     LD (DE), A

     INC E

     LD A, L

     LD (DE), A

     DEC E

     INC D

     POP HL

     INC H

     DJNZ PRGO

     POP DE

   If the font is limited by 0, then remove the LD
B, 8, and DJNZ PRGO to replace JR NZ, PRGO.

   Register C should contain 7,5,3 or 1
and 7 corresponds to the zero coordinate
letters inside the familiarity (x mod 8 = 0). Letters in
font 256, and they are all pressed to the left
(Can be shifted by one point right). As
have to change C:

     LD A, C

     SUB 6

     JR NC, $ +5

     INC E

     AND 7

     LD C, A


   And, finally, touch on all the already zadolbavshego
ZXrevyushnogo address calculation letters in ROM:

      Was: So:

     LD L, A LD L, A

     LD H, 0 ADD HL, HL

     ADD HL, HL LD H, 15

     ADD HL, HL ADD HL, HL

     ADD HL, HL ADD HL, HL

     LD BC, 15360

     ADD HL, BC

   Make sure you all my life hung to deceive