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<1234567…34>
  • RLD - zero-flag resultI have very rarely found need to use the RLD instruction, well, actually just this once, but everything I can find on it says that the zero-flag is s…

    ... on it says that the zero-flag is set "to reflect the ... be whether the accumulator is zero or not after the action ...
    bobs bobs March 2014 Development
  • Key press to ASCII valueI need a bit of code that will give me an ASCII value when the key is pressed. I only really need a-z. I tried using the following code but it only s…

    ... it only seems to return zero or 32 if space is ... =FF if no key pressed, Zero flag reset if more than one ... key pressed else zero set and A=D
    Mr Millside Mr Millside July 2005 Development
  • Tutorial - learn machine code in 30mins[B][I]Message from the moderators[/I] - bigjon has requested that readers' attention be drawn to a better version of this tutorial, one which is easi…

    ... for jump relative if not zero. It skips over the ... carry, and set the carry flag to zero.
    'or' compares ... all the digits are zero, then the zero flag will be set, ... and Repeat (until bc is zero).
    Replace line 53 ... bit and sets the zero flag if it is 0)< ...
    bigjon bigjon November 2009 Development
  • A tidy loader for minigamesThe minigame competition doesn't permit the use of separate loaders like [code]10 LOAD "": RAND USR 32768[/code] The loader must be included in the b…

    The minigame competition doesn't permit the use of separate loaders like
    [code]10 LOAD "": RAND USR 32768[/code]
    The loader must be included in the byte count.

    In an attempt to save as many bytes as possible, people have written ...
    ajmoss ajmoss June 2010 Development
  • BREAK from GOSUBHere's another one. Just in case you wanted to break out of multiple GOSUB levels with a single command, here's a routine to do it, tested on all mod…

    ...
    INC B ; 4 ;reset Zero flag
    EXX ; 217
    NOGSUB ...
    Battle Bunny Battle Bunny December 2011 Sinclair Basic
  • Inefficient code in ROM, from ram-check to RAM-DONEHere is the inefficient code: [CODE] ;; ram-check L11DA: LD H,D ; Transfer the top value to the HL register LD L,E …

    ... ; back to RAM-READ if zero flag was set.

    ;; RAM ... ; back to RAM-READ if zero flag was set.

    ;; RAM ...
    antoniovillena antoniovillena April 2012 Development
  • MOVE_M Object Movement Manager for BASICAs moving things around on the screen is usually the slowest part of a game written in BASIC, I've been pottering around with this routine to handle …

    ... the DE register and the Zero flag
    ;indicate which keys are ...
    Battle Bunny Battle Bunny September 2013 Sinclair Basic
  • z80 less than and greater thanI am writing a keyboard routine where the pressed key code number is held in A. I only want to action the number key presses 1 to 9 (codes 49-57) so …

    ... 49

    The zero flag is set if the numbers ... equal
    The carry flag is set if the ... br /> Neither the zero flag or carry flag is set if A ... the condition that the Zero flag and carry flag is clear? Would ... a,57 ; The carry flag is set if the number ...
    Speccy_James Speccy_James February 2014 Development
  • Detecting +3 / +2AWhat's a simple but reliable way to detect if code is running on a +2A/+3? My first though was to try switching to ROM2 and then checking for the …

    ... ; test for stored 0
    ; zero flag set means we're on ...
    FishFinger FishFinger December 2017 Development
  • Bug in ZX SpinADD HL,BC sets Z-flag when adding #faff and #501. By design ADD HL,rr does not set zero flag.

    ADD HL,BC sets Z-flag when adding #faff and #501.

    By design ADD HL,rr does not set zero flag.
    Dr BEEP Dr BEEP April 2019 Emulators
  • Remainder (Mod) calculationsI've been figuring out how to calculate remainders after integer division by a constant divisor k (A mod k = A % k). I found that for most small di…

    ... = original integer from A
    Zero flag (ZF) is set if k ...
    Magne Magne October 2021 Assembler
  • Assembler code from tutorial, problem!I was wondering if anyone could help me decipher this z80 assembler code? ORG 60000 LOAD 60000 EA60 21BCEA LD …

    ... , so cp 8ah results in zero flag set
    in all other ...
    Mikie Mikie August 2001 Sinclair Miscellaneous
  • Assembler code from tutorial, problem!I was wondering if anyone could help me decipher this z80 assembler code? ORG 60000 LOAD 60000 EA60 21BCEA LD …

    ... the contents of the zero flag
    if the zero flag IS set (i ... of the preceding operation WAS zero), then the program counter will ... jr nz
    if the zero flas IS NOT set (i ... the preceding operation WAS NOT zero), then the program counter will ...
    Mikie Mikie August 2001 Sinclair Miscellaneous
  • Machine Code ChallengeHere's a challenge for all you Z80 programmers. Points to be awarded for elegance and brevity. (I haven't got the solution either) HL addresses the …

    ... ,B
    OR A ; Load zero flag.
    RET Z ; Return from ... reset bits.
    Skip CPI ; Zero flag reset when a reset bit ... .
    PUSH AF ; Save carry flag.
    OR C ; OR A ... .
    POP AF ; Restore carry flag.
    RET
    Fraser Fraser July 2002 Sinclair Miscellaneous
  • Machine Code ChallengeHere's a challenge for all you Z80 programmers. Points to be awarded for elegance and brevity. (I haven't got the solution either) HL addresses the …

    ... 4 OR A ; Load zero flag.
    8007 C8 5 ... 8013 EDA1 16 Skip CPI ; Zero flag reset when a reset bit ... POP AF ; Restore carry flag.
    802B 23 6 ...
    Fraser Fraser July 2002 Sinclair Miscellaneous
  • Anyone for a hacking challenge ?I have to get the DSK version of Tomahawk to work. It uses the well-known Digital Integration "SECURITY CODE" lock just like in Bobsled, ATF, etc. Th…

    ... Z, E921 ie. If the Zero flag is set jump to our ... it's possible that the Zero flag being set could mean that ...
    BadBeard BadBeard August 2003 Sinclair Miscellaneous
  • Z80 coders compoIf you're interested in Z80 coders compo, visit my page [url="http://mbr.nm.ru/compo.html"]http://mbr.nm.ru/compo.html[/url]

    [quote]Cyborg, your code isn't optimal![/quote]

    I know but I did have to rewrite it quickly before the deadline after a crash. I almost forgot to update the zero flag at all.
    cyborg cyborg November 2003 Development
  • Collision DetectionHi everyone, This is my first post on WOS. Like most people here I owned a Spectrum when a teenager. At that time I was quite heavily into programmin…

    [code]
    dec a
    jp c,dosomething
    [/code]




    [/quote]


    DEC A
    won't give a carry, only Zero flag.
    Dr BEEP Dr BEEP September 2004 Development
  • Collision DetectionHi everyone, This is my first post on WOS. Like most people here I owned a Spectrum when a teenager. At that time I was quite heavily into programmin…

    ... 't give a carry, only Zero flag.
    [/quote]

    Bah ...
    AndyC AndyC September 2004 Development
  • Mnemonic HELPREFERENCE: [url="http://www.geocities.com/SiliconValley/Peaks/3938/z80_home.htm"]http://www.geocities.com/SiliconValley/Peaks/3938/z80_home.htm[/url…

    ...
    When you get ZERO, the zero flag is set, so
    this ...
    Dr BEEP Dr BEEP October 2005 Development
  • After roughly 22 years can you help?Hi, A long one this but here goes. Roughly 22 years ago (i was 14 if i remember right) i got a 48K speccy for christmas of my dad it was awesome an…

    ... (only) and checks if the Zero Flag has been set before jumping ...
    Ian Hamilton Ian Hamilton November 2005 Sinclair Miscellaneous
  • What happens during a reset?I always used to wonder about this, but only thought a bit more about it last night when noticing after all these years what actually happens. Obvio…

    ... decrement was used. If the zero flag was not set, then the ... ' was used and if the zero flag was set on the first ...
    Geoff Geoff February 2006 Sinclair Miscellaneous
  • What happens during a reset?I always used to wonder about this, but only thought a bit more about it last night when noticing after all these years what actually happens. Obvio…

    ... ' was used and if the zero flag was set on the first ... like they're reset to zero - or maybe they're all ...
    Gwyn Gwyn February 2006 Sinclair Miscellaneous
  • FP Calc QuestionWhen using the FP Calc (RST 28h) to perform a subtraction how do you find out what the sign of the result is? ie. +/-. For example if I stack two va…

    ... FP-TO-BC then the zero flag will be set Z if ... if negative.
    The carry flag will be set if over ...
    Geoff Geoff March 2006 Development
  • Pixel Explosion CodeJust a little snippet to cause explosive effects. It uses table lookups for the screen address, and can handle up to 32 pixel particles. A particle…

    you can also use "and a" for the same purpose.
    it is a nice quick way to set the zero flag.
    Kiwi Kiwi September 2006 Development
  • How does interrupts work?I am a little confused regarding the interrupts on the Spectrum. If I have some hundred bytes of machine code started with, say, [B]RANDOMIZE USR 300…

    [QUOTE=Rickard;193535]

    [CODE]xor a ; black border[/CODE]

    I have always wondered if this instruction actually can be used for anything else than setting A to 0? :smile:[/QUOTE]

    Reset Carry Flag and set Zero flag!
    Dr BEEP Dr BEEP May 2007 Development
  • How does interrupts work?I am a little confused regarding the interrupts on the Spectrum. If I have some hundred bytes of machine code started with, say, [B]RANDOMIZE USR 300…

    [QUOTE=Dr BEEP;193542]Reset Carry Flag and set Zero flag![/QUOTE]

    But it can never do anything useful with the XOR instruction itself?

    Could the opcode have been "Clear A and Carry, set Zero"? :-)
    Rickard Rickard May 2007 Development
  • Question on Z80 R/W cycles.Snipped from the complete spectrum ROM disassembly: [CODE] Now the memory is checked. 11DA RAM-CHECK LD H,D Transfer the value…

    ... />
    The Zero here refers to the zero flag in the F ... of hl are decremented to zero. The JR Z instruction ... if and only if the zero flag is set - the memory ... having DEC (hl) to zero, you had changed the value ... it's checking the zero flag in F rather than ...
    Arjun Arjun August 2007 Sinclair Miscellaneous
  • Question on Z80 R/W cycles.Snipped from the complete spectrum ROM disassembly: [CODE] Now the memory is checked. 11DA RAM-CHECK LD H,D Transfer the value…

    ... decreases it. I presume the zero flag is set then, before the ... re-read again and the zero flag set accordingly.

    I ...
    dmsmith dmsmith August 2007 Sinclair Miscellaneous
<1234567…34>

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