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<1234567…34>
  • When would you use LD A,R ?Can anyone tell me a practical use of LD A,R and LD R,A I am confused when you would need to use it? Cheers

    Can anyone tell me a practical use of LD A,R and LD R,A I am confused when you would need to use it?

    Cheers
    robpearmain robpearmain November 2009 Development
  • Using R as a loop counterThis is just something silly I've found a while back. xD [b][How-to][/b] Setup your routine like this:[code] ld a,X ;see below ld r,a loop ;your …

    ... /> ld r,a
    loop
    ;your routine here
    ld a,r
    ld a,r: jr nz,loop' commands) ... ld r,a
    .l2
    nop
    inc b
    ld a,r
    jr nz,.l2
    ld a,b
    out (#FE),a ...
    Hikaru Hikaru October 2012 Development
  • R registerI'm cross-posting this as a spin-off of a [url="http://www.worldofspectrum.org/forums/discussion/52748/zx-spectrum-cartridges/p2"]thread in "Hardware…

    ... from an LD R, A instruction.
    The data in the refresh counter is ... fetch. Hence R register can be considered a simple counter (instruction counter). It makes ... tested on), increment twice for "LD A,R" instruction, and once for all ...
    RMartins RMartins June 2016 Emulators
  • DEC BC/LD A,B/OR C/JP NZ,loopyesterday i saw nice trick:[code] dec bc ld a, b or c jp nz, loop can be replaced (bc starts >255, short jump) by: dec bc inc b djnz loop [/code] …

    yesterday i saw nice trick:[code]

    dec bc
    ld a, b
    or c
    jp nz, loop

    can be replaced (bc starts >255, short jump) by:

    dec bc
    inc b
    djnz loop
    [/code]
    ..nice
    Fikee Fikee February 2005 Development
  • Any played F.E.A.R? (New PC Game)I know a lot of you played Half-Life2 when it came out so I would gather a guess that a lot of you have been looking forward to this too (it's been a…

    I know a lot of you played Half- ... so I would gather a guess that a lot of you have ... it's either F.E.A.R. or Quake 4 but I ...
    Vampyre Vampyre October 2005 Chit chat
  • W.A.R. (missing artist?)[URL="http://www.worldofspectrum.org/infoseekid.cgi?id=0005620"]W.A.R.[/URL] NAK or MAK lower right ... might be MAK = Mark A. Jones? (already credi…

    ... /infoseekid.cgi?id=0005620"]W.A.R.[/URL]

    NAK or ... right ... might be MAK = Mark A. Jones? (already credited)

    A.R..gif[/img]
    ZnorXman ZnorXman October 2009 Infoseek database
  • Contention: LDI vs LD (ss), rAccording c.s.s. FAQ: instruction LD (ss),r breakdowns as pc:4,[b]ss:3[/b] and LDI as pc:4,pc+1:4,hl:3,[b]de:3,de:1 x 2[/b] can anyone explain why …

    ... . FAQ:

    instruction LD (ss),r breakdowns as pc:4,[b ...
    Fikee Fikee February 2011 Development
  • Canny use of the 'r' register?Seeing Sokurah's code in the [URL="http://www.worldofspectrum.org/forums/showthread.php?p=583188#post583188"]crunch sound thread[/URL] has made me th…

    ... made me think about the r register.

    ... I've used this a fair bit myself as an ... way to get a 'random' number eg:

    ld a,r
    ... so presumably better than eg LD A,(23672) (though much much ... how it's a bit of a blunt instrument as ...
    R-Tape R-Tape November 2011 Development
  • New WIP from Kabuto Factory: A.R.C.O.S.Hi everybody! After a long time in silence (...you know, life and its commitments...), we're coming back with new WIP for Speccy: A.R.C.O.S., a new …

    Hi everybody!

    After a long time in silence (...you ... new WIP for Speccy: A.R.C.O.S., a new "brick'em ... [/url]

    Here goes a screenshot ;)

    [IMG]http ...
    Baron Ashler Baron Ashler February 2012 Brand new software
  • New game from Kabuto Factory: "A.R.C.O.S."Hi everybody! After almost one year in production (...well... not so much... :roll:), we've got new release: A.R.C.O.S., a brick'em all with some sh…

    ... got new release: A.R.C.O.S., a brick'em all with ... possible. You control A.R.C.O.S., a spaceship which bounces an ... lives. In addition, A.R.C.O.S. has a laser blast with ... extra ammo when you clear a stage, depending on the ... our fellow RALF (thanks a lot, dude!)
    Baron Ashler Baron Ashler October 2012 Brand new software
  • A FAQ from a Z80 datasheet may reveal some up-to-now unknown behavioursA fellow member of the zonadepruebas.com forum has just mailed this PDF to me. [url]http://www.atc.us.es/~rodriguj/zilog_z80_faq.zip[/url] It's an e…

    A fellow member of the ... It's an exceprt from a 1995 Z80A datasheet. This FAQ ... do cycle step on a NMOS o CMOS chip?< ... - What happens if a NMOS Z80 suffers a negative spike? (those pesky ... behaviour of interrupts during a LD A,I or LD A,R instructions? (this may ...
    mcleod_ideafix mcleod_ideafix October 2013 Hardware
  • Simple text scrolling routine...I'm having trouble writing a very simple text scroller, the idea is to use the ROM printer routine to print 32 characters each time the routine is ca…

    ... /> ld a,(counter)
    inc a ;increase
    ld (counter),a ;update counter with new number
    ld (point ...
    ld hl,23264
    ld b,64
    loop
    ld a,r
    and 5
    inc a
    ld (hl),a
    inc ...
    daveysludge daveysludge September 2014 Development
  • Cobra - scrollingHi everyone, I have been studying some of the code in Ocean' Cobra game using a debugger, in the hope of improving my own scrolling routines. In cas…

    ... br /> [code]

    loop ld a,r
    ret m
    jr ...
    Remember that R is a 7-bit counter only; it's top ... is written to it with LD R,A. Hence the above will ... if the top bit of R is unset or not at ... if the top bit of R is set.

    ...
    Philip Kendall Philip Kendall October 2004 Development
  • Sprite adviceHello. So, I'm slowly getting to grips with Z80 assembly - currently equal parts frustration and enjoyment. Now looking for some advice to help shift…

    ... using a ld a,r command to grab a number from the memory refresh counter. Only ... all.

    Is there a quick way of generating random ... Occasionally each sprite will do a weird sort of warp effect ... bottom of screen directly after a HALT?

    Many ...
    48K 48K May 2006 Development
  • Sprite adviceHello. So, I'm slowly getting to grips with Z80 assembly - currently equal parts frustration and enjoyment. Now looking for some advice to help shift…

    ... a ld a,r command to grab a number from the memory refresh counter ... br />
    Yeah, not a very good random number generator ... on PC, quite a gonzo-routine on Z80 ... br /> ld hl,(int_seed)
    ld a,h
    add a,a ;Set highest ...
    Alcoholics Anonymous Alcoholics Anonymous May 2006 Development
  • Adjusting your code for screen refreshingOk, I'm aware that I should know it already after writing 5 Spectrum games in machine code but interrupts and screen refreshes were always my weaker …

    ... ?t=27280[/url] "what is LD A,R used for?").

    Once ... become set, instead of issuing a HALT. If your precalculations take ... have your interrupt routine decrease a framecounter, setting bit 7 of ... your sprites, reset the frame counter to 2, 3 or whatever ...
    csmith csmith November 2009 Development
  • Auto generated spritesLooking around for some graphics I came across [url]http://blog.disktree.net/?p=19[/url] , one of several such pages. Need the odd 8x8 UDG or two (…

    ... takes the contents of the r register, halves it & mirrors ... a
    ld (23560),a ;last key pressed
    ld b,0 ;counter
    loop ld a ... keep getting key pressed
    ld a,r ;r register always ticking round
    R-Tape R-Tape December 2011 Development
  • Help needed... RND in machine codeI have been battling away trying to convert a simple BASIC routine (below) to machine code, but to no avail. The routine is used to fire 2 bullets a…

    ... do this.

    [CODE] ld a,r ;constantly cycled number,Patricks xor ... :-D

    [CODE] ld a,r ;random number
    and 31 ... but there is also the ld a,r or ld a,(23672) amongst others. For ... of which was based on a counter that was based on how ...
    R-Tape R-Tape July 2012 Development
  • New Game(s): Sir Ababol 2 and Sir Ababol DXHere is our own Christmas Present from Mojonia! We weren't going to release these games (at least, by the moment) but we decided just yesterday to fi…

    ...
    ld b,number_of_keys
    dklp push bc ;save counter
    ... /> ;
    little_noise
    ld b,0
    lnlp ld a,r
    and 248 ...
    out (254),a
    djnz ... g. in game LD HL,key1, LD A,(HL), IN A,(254), INC HL ...
    R-Tape R-Tape January 2015 Brand new software
  • ZX Spectrum CartridgesI have been thinking of "cloning" ZX Cartridges for a while (case, board and silicon skirt), to be able to make new releases or replace damaged cartr…

    ... from an LD R, A instruction.
    The data in the refresh counter is ... fetch. Hence R register can be considered a simple counter (instruction counter). It makes ... tested on), increment twice for "LD A,R" instruction, and once for all ...
    RMartins RMartins June 2016 Hardware
  • Short Z80 QuizQ1) Which program gives different result ? A) XOR A ADD A,A B) XOR A ADC A,A C) SCF ADD A,A D) SCF ADC A,A Q2) What is the equivalent of NEG …

    ... of NEG ?

    A)
    LD A,-1

    B)

    A)
    LD B,10
    LD HL,60000
    DEC BC
    LD A,B
    OR C

    Q8) What value holds A after LD A,R ?

    Q9) What ...
    Dr BEEP Dr BEEP July 2002 Games
  • InterruptsA small piece intended for the FAQ. Comments, corrections, additions welcome. Notably: * How long does the 48K ULA hold /INT low? * What happens i…

    ... can be missed entirely. A second effect can occur with ... :

    * If a LD A,I or LD A,R (which copy IFF2 to ... interrupt' feature is known as a retriggered interrupt.

    ... it was zero (thus causing a reset). However various peripherals, ...
    Philip Kendall Philip Kendall July 2004 Development
  • Mysterious bit of codeHi everyone, I found the follow piece of code in a game and was wondering what it does. ld bc,40ffh ld e,40h loop ld a,r …

    ... follow piece of code in a game and was wondering what ... /> ld bc,40ffh
    ld e,40h
    loop ld a,r
    in a,(c ... ages, and then returns.
    A delay of some kind, I ...
    dmsmith dmsmith August 2004 Sinclair Miscellaneous
  • Programming MC : first stepsIsn't nice to collect all kinds of short routines to help making the first steps into MC for everyone who never touched MC? What I mean is mostly th…

    ... on screen
    A simple Randomgenerator (not LD A,R)
    Other tips and ... tricks.
    Reading a value from a table ... number
    ld a,h
    and #3f
    ld h,a ; but keep ...
    Dr BEEP Dr BEEP August 2005 Development
  • Urgent Help needed to fix this: calling all machine code gurusI am currently trying to write tutorials on the amazing Orfeus music composer by Proxima which allows you to do multi channel music through the beepe…

    ... /> ld a,#00
    ld (l8994+1),a
    ld (l899d+1),a
    ld (l89e3+1),a ... a
    ld (l8bd9+1),a
    inc a
    ld (l898F+1),a
    ld a,(l8994 ... ),a
    ld e,a
    ld a, robpearmain robpearmain November 2006 Development
  • RET MHello. I?ve seen in the Joffa game SAUCER a kind of loop like this LOOP LD A,R RET M JR LOOP I do know what this loop mea…

    ... this


    LOOP LD A,R
    RET M
    JR ...
    climacus climacus July 2012 Development
  • Machine code loopsThis might sound a bit daft, but I,ve forgotten how to do loops using th 'b' register... I want to loop this x mount of times: [CODE]ld a,r and 6 i…

    This might sound a bit daft, but I,ve ... /> [CODE]ld a,r
    and 6
    inc a
    ld (aa+1),a
    daveysludge daveysludge August 2012 Development
  • Accidental rainbow effects.. How do I adapt?I've somehow bizzarrely created a rainbow text effect on my title screen by accident. The title was just supposed to flash different colours whilst …

    I've somehow bizzarrely created a rainbow text effect on my ... ]org 60000
    loop ld a,239
    in a,(254) ;check keys ... /> start ret ;return
    flash LD A, R ;flash routine
    AND 67 ... A
    LD B, 14
    LD DE, 22665
    lp2 LD (DE), A
    daveysludge daveysludge February 2013 Development
  • Idk>le me browsing through some game's code >..... [code]61A8 F5 push af 61A9 3EFF ld a,FF 61AB D37F out (7F),a 61AD D33F ou…

    ... ED57 ld a,i
    61DA 67 ld h,a
    61DB ED5F ld a,r
    61DD 6F ld l,a
    ld i,a
    62A9 7D ld a,l
    62AA ED4F ld r,a
    Hikaru Hikaru June 2013 Development
<1234567…34>

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