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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 -
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 ... -
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…
... as programmed, resulting from an LD R, A instruction.
The data ... fetch. Hence R register can be considered a simple counter ( ... on), increment twice for "LD A,R" instruction, and once for ... base emulation, and hence this bug propagated ?
... -
InterruptsA small piece intended for the FAQ. Comments, corrections, additions welcome. Notably: * How long does the 48K ULA hold /INT low? * What happens i…
... consequences:
* If a LD A,I or LD A,R (which copy IFF2 to ... interrupt' feature is known as a retriggered interrupt.
... an NMI, and secondly a bug in the ROM's NMI ... it was zero (thus causing a reset). However various peripherals, ... -
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 -
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 ... -
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] -
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 ... -
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 ... -
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 ... -
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!) -
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 ... -
ZEsarUX 6.1 RCHi I have uploaded a new beta version of ZEsarUX. This is ZEsarUX 6.1 RC so next version will be a final stable version :) You can download it fr…
... emulation (experimental)
Added a fast spectrum core (with some ... Improved menu interface:
* added a setting to limit menu event ... never see it ;)
Fixed bug on Z80 cpu core, iff2 ... reading it by using LD A,R and LD A,I affected many demos< ... -
ZEsarUX-7.0Hi! I have uploaded a new ZEsarUX stable version :) This is ZEsarUX 7.0 There are a lot of new features added, more than ever! You can downl…
... br />
I have uploaded a new ZEsarUX stable version :)
* Added a setting to start TBBlue directly ... Dandanator rom menu
Fixed bug on Z80 cpu core, iff2 ... reading it by using LD A,R and LD A,I affected many demos
InterruptsA small piece intended for the FAQ. Comments, corrections, additions welcome. Notably: * How long does the 48K ULA hold /INT low? * What happens i…
... consequences:
* If a LD A,I or LD A,R (which copy IFF2 to ... [/quote]
This allows for a RETI instruction after EI. Another ... interrupt' feature is known as a retriggered interrupt.
[/quote ... an NMI, and secondly a bug in the ROM's NMI ...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…
... started using a ld a,r command to grab a number from ... ]
Yeah, not a very good random number generator ... compact on PC, quite a gonzo-routine on Z80. ...
ld hl,(int_seed)
ld a,h
add a,a ;Set highest ...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…
... time between repeated runs is a repetitive length (some lengths being ...
ld h,a
ld a,r
xor h
ld (seed),a
[/ ... the warp effect isn't a bug :) - I think it is ... time.
---
A different question to all and ...Sprites masterclassHi All, You guys are probably tired of explaining sprites but I'd like to clarify a few things if possible. I've sorted the vertical aspect of scro…
... and it's far from bug free):
[CODE]org ...
call nc,mpr
ld a,r
cp 20
call ... xor a
ld a,(ix+0)
rra
ld (ix+0),a
ld a ... ,(ix+1)
rra
ld (ix+1),a
ld a ...Bug in Super Wonder Boy in Monsterland?Hello!:smile: This game seems to have a bug that prevents finalize. The dragon that is in the last level, it is impossible to kill.Remains static.No…
... of fireballs shot
ld a,r
and 1
ld a,r
and 3
add a,e
ld e,a
ld a ... />
;=============================================================================
;cpc bug in scrolling end message
SCF/CCF flags - new discoveryI can't believe that no one is interested in discussing the additional, previously undocumented internal state of the Z80 CPU I have discovered recen…
... bug in the behaviour of P/V flag during the commands LD A ... , I and LD A, R (see [url]http://www ... /V flag is reset. This bug can be observed on NMOS ... is a must, I believe. And given that the described bug is ...SCF/CCF flags - new discoveryI can't believe that no one is interested in discussing the additional, previously undocumented internal state of the Z80 CPU I have discovered recen…
... as long as the IFF2 bug is modelled by emulators correctly ... the previous instruction was an LD A,R (or LD A,I) and modify the ... acknowledgement after we've executed LD A,R only to have the ... be 'DI; EI; LD A,R'. I would expect 'LD A,R' to behave as normal ...SCF/CCF flags - new discoveryI can't believe that no one is interested in discussing the additional, previously undocumented internal state of the Z80 CPU I have discovered recen…
... bug in the behaviour of P/V flag during the commands LD A ... , I and LD A, R (see [url] ... flag is reset. This bug can be observed on ... Every time you enter a critical section, you need ... br /> (Note to self: needs a-fixin)
Even ...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…
... as programmed, resulting from an LD R, A instruction.
The data ... fetch. Hence R register can be considered a simple counter ( ... on), increment twice for "LD A,R" instruction, and once for ... base emulation, and hence this bug propagated ?
...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 ...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 ...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 ...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
November 2006
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
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
