Questions tagged [assembly]
Assembly languages in general, of any architecture. Use with the particular processor’s tag as appropriate.
230
questions
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Help understanding TAIPAN source code for the Apple II
I am trying to run the source code found at https://taipangame.com/BASIC.txt on Epple 2 (with Apple II+ roms) to eventually run on my own Apple II+, but the program keeps crashing.
First, I used a ...
- 83
17
votes
3
answers
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Does this 1978 code for a 6800 really clear ALL of memory?
On page 43 of the October 1978 Dr. Dobb's Journal (reprinted in Volume 3 Page 425 Issue 10 Number 29) is a letter to the editor giving three 6800 routines to clear ALL of memory, stating...
Routine ...
- 171
8
votes
1
answer
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C64 char screen plot routine - not clear about reason for logical OR
I'm trying out some 6502 assembly language, specifically using Kick Assembler. I have the following routine that just sticks a character on the text screen at a specified x and y, it's taken from the ...
- 3,857
5
votes
1
answer
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Can anyone help me identify what 6803/6303 development tools might have been used to build this program?
I've been doing some hobby work reverse-engineering vintage synthesizer ROMs from the early 80s, and I'm curious about what kind of development tools the original engineers may have used. Normally ...
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6
votes
0
answers
277
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Sending DOS commands in assembly on my C64
Consider the following Basic program for the C64.
10 OPEN 15,8,15
20 PRINT#15, "I"
30 CLOSE 15
This classic gem simply opens the 'command channel' and sends the DOS 'init' command to the ...
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4
votes
1
answer
227
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Documentation for the SALUT preprocessor of the IBM Macro Assembler 2.0
The IBM Macro Assembler 2.0 included the SALUT program, which was a preprocessor for assembly language for structured programming. It was also included in the IBM Macro Assembler/2.
I am looking for ...
2
votes
0
answers
324
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Trying To Understand DOS Game Assembly Instructions [closed]
I am trying to understand assembly language instructions, for a DOS Game. I have looked at the following Link :- https://atrevida.comprenica.com/atrtut07.html
reading about how VGA Graphics work in ...
- 21
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0
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Did the Soviets need industrial espionage to get IBM software pre-1970?
Due to lack of the OS-level file system on the BESM-6, and to deficiencies of data visualization tools which could help people decide which blocks of a system disk could be reused (the line of ...
- 18.3k
12
votes
2
answers
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Floppy drive detection on an IBM PC 5150 by PC/MS-DOS
The only functions of INT 13h available for pre-XT systems are the first six, from AH=00 to AH=05 (see here and here)
Since function AH=08 (Get current drive parameters) is unavailable, how does PC-...
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3
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2k
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What's the convention for < > low/high-byte in 8-bit assembler?
It's a little hard to Google for greater-than and less-than symbols in assembler math...
If you saw, let's say, 6502 code like...
lda #>SOME_LABEL
or Z80 code like...
ld a,>SOME_LABEL
...would ...
- 331
1
vote
1
answer
197
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Interfacing with the Commodore 64 IEC Serial Port using Assembly
I'm struggling a bit to find relevant documentation on this subject when it comes to using just assembly. All I've found is either irrelevant or for BASIC. My goal is to be able to send and receive ...
- 21
6
votes
1
answer
375
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Which CPU was the first to clear the carry and overflow bits after performing logical operations?
As I work on implementing support for old architectures for the Reko decompiler (https://github.com/uxmal/reko) I notice over and over how consistently most 1980's CPUs echo a pattern.
Since an ...
- 465
15
votes
3
answers
3k
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Difference between machine language and machine code, maybe in the C64 community?
I've always been sure that "machine language" and "machine code" are totally synonymous and mean programming directly in the language the machine understands, whether in binary, ...
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11
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5
answers
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Creating 8086 binary larger than 64 KiB using NASM or any other assembler
For fun I'm developing an IBM PC emulator. I would like to test all instructions to see if I implemented them correctly. For most instructions this is straight forward, for "FAR CALL/JMP" it ...
10
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4
answers
2k
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Assembly delay function for C64
I've written a delay function that simply counts the times the screen raster line reaches a particular value.
// zero page addresses
.const delayFrames = $00fa
.const delayCounter = $00fb
// =...
- 255
5
votes
5
answers
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Are there any statistics or data showing how much more productive the C programming language is compared to x86 assembly language?
I found out today that a large project like Microsoft Windows 1.0 took 80 man-years to develop. And this one was written in x86 assembly language.
Is there a form or rule of thumb that states how much ...
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16
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4
answers
2k
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Is it possible to detect a CGA card on an IBM PC 5150 by write/reading the Motorola 6845?
I am trying to programatically detect the CGA card on old IBM 5150-ish PCs.
The Paku Paku game source code doesn't directly detect it. The strategy is to detect VGA, EGA, Tandy, PCJr, etc etc, then if ...
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14
votes
3
answers
2k
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Help porting nasm code down from 386 to 8088 (shifts by more than 1 bit)
I have been writing some small asm COM program using Netwide Assembler (nasm), but am having trouble getting it to run on 8088 emulators like PCjs. I could use some help translating the assembly "...
- 465
10
votes
2
answers
753
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How can I avoid overflowing R_SPARC_13 relocations when writing SPARC assembly?
For fun I'm trying to create an assembly program for Sun Solaris on SPARC. I'm emulating the system with QEMU.
My test assembles fine, yet linking fails with "relocation error: R_SPARC_13". ...
31
votes
6
answers
3k
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Managing registers/memory effectively on the Z80
I've been writing assembly for the Z80 for some time, lately. Initially, I had no experience with working with 8-bit processors, but after going through a tutorial for my platform and spending a lot ...
- 455
11
votes
2
answers
564
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IMPI Instruction set: is there any reference?
I've had an IBM 9404 B-10 for some time and I'm curious about its assembly language. I'm fully aware the AS lines were designed with portability in mind as much IBM didn't seem to provide assembly ...
- 703
6
votes
2
answers
245
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6502 Assembly on Apple IIe: GETLN fails with 'syntax error' under ProDOS
I'm writing a text adventure in assembly for the Apple IIe (using Merlin). I'm also using ProDOS 8 v2.0.3. At some point, I have a subroutine to read user input from the keyboard using the GETLN1 call....
3
votes
1
answer
346
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Is RosAsm assembler self-hosting?
I have a few questions about the RosAsm assembler (not in active development anymore) by René Tournois:
Is/was there a command-line tool (i.e. without a GUI) included to generate executable programs ...
- 1,435
15
votes
4
answers
2k
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Looking for an open source DOS .com program written in assembly
I'm writing a NASM-compatible assembler targeting the Intel 8086, and I'm looking for an existing open source program written in assembly, with which I can showcase the capabilities (and understand ...
- 1,435
10
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3
answers
2k
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How to write text in MODE 0x13?
I have read How to write directly to video memory using "debug.exe" in MS-DOS? and I know how to write text to video memory in mode 0x3 but I can't figure out how to write text to video ...
- 345
10
votes
11
answers
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Towards people who were there, what programs did you use to develop applications for the IBM 5150? [closed]
I want to get into programming on old MS-DOS systems, before then going to older DOSs like CP/M. However, while programming for MS-DOS I'd like to also use era-appropriate software, both for the ...
- 109
7
votes
1
answer
421
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Why didn't the CP/M-86 assembler support traditional macros?
The ASM86.CMD assembler Digital Research shipped with CP/M-86 provided only code-macros, a limited type of macros for creating new instructions through a small set of specific directives. Why didn't ...
- 1,313
24
votes
1
answer
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Where can I find the debate around snow-free screen updates mentioned in the Zen of Assembly Language?
Michael Abrash's book Zen of Assembly Language: Volume I (1989) contains a reference to a column in a computer magazine, though the actual source is not cited.
From the text:
I recall a debate in the ...
- 1,287
0
votes
1
answer
250
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Apple II mixed mode cursor placement
I've been playing on my recently resurrected Apple IIs, a //e, IIc, and IIgs (mostly the //e), tinkering with assembly.
I'm reading the paddles and plotting a colored block on the screen, kind of an ...
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2
answers
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Asking explanation of 65C02 assembler code
From Gary B. Little's "Apple ProDOS: Advanced Features for Programmers", pages 176 - 188:
"Since the ONLINE command handler is not inherently relocatable, all
references to internal ...
- 93
6
votes
2
answers
461
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SciTech's SVGAKit seems to be incomplete
I'm trying to get into MS-DOS development for fun, and I'd like to use SciTech's SVGAKit library. The last version of it is still downloadable via the Internet Archive here. However it seems to be ...
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8
votes
1
answer
280
views
Using the (An)+ to Memory addressing mode when address register is pointed to ROM causes Sega Genesis DMA to fail
This is a weird one, and I haven't found it documented anywhere. I was testing Sega Genesis DMA during scanline interrupts and found something very odd. When writing to VDP_CTRL to initiate DMA, if ...
- 1,638
5
votes
5
answers
472
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Chaining IRQs in x86 ROM code
Objective Summary: I need to write a sleep() function to be used in 8088 (PC/XT ISA) ROM code with 1 ms resolution. Though the question can be more generalized to chaining INTs with data in different ...
- 1,287
15
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3
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Running CP/M on my own Intel 8080 emulator
I recently finished writing an emulator for the Intel 8080, having passed all of the usual test suites, and wanted to try running an actual OS on it (such as CP/M). I'm aware that I would have to ...
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26
votes
3
answers
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Why are the Intel 8080's rotate instructions called opposite to intuition?
The Intel 8080 has two pairs of instructions for rotating the value of the accumulator -- RLC/RRC and RAL/RAR.
One of them shifts the 8 bits in the accumulator circularly, writing out into the carry ...
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6
votes
1
answer
469
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How do I read a port value using Turbo Pascal inline code on CP/M?
After successfully using port[0] to read a port value in Turbo Pascal, I thought I'd try to understand how to do this using inline assembly/machine code.
I'm able to write to the port (my OutPort ...
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38
votes
3
answers
5k
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Why are assemblers called assemblers?
We tend use the term assembler as if there is a fundamental implication of being different from a compiler. This disparity is usually taken as a fact, no matter how sophisticated or primitive either ...
- 213k
10
votes
3
answers
2k
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Is there an equivalent of "#pragma once" in RGBASM (Gameboy DMG assembly language)?
So I am really just starting out in my assembly coding adventure. I have a little bit of knowledge of C/C++ but nothing too advanced yet.
But I also used to do a tiny bit of Z80 assembly, and I wanted ...
- 203
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votes
1
answer
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If I build a new CPU architecture, how would an OS like Linux know how to run it? [closed]
I am trying to build a CPU from scratch (from NOR gates) in an emulator first, then on breadboard. (Inspired by nand2tetris and Ben Eater)
Just trying to understand how things work.
Now, as my CPU ...
2
votes
2
answers
363
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From an electrical and software engineering perspective, ignoring available software, should I go for the Z80 or 65C02? [closed]
This might be a weird title but I noticed that recommendations for one over the other usually go into a direction that is not too helpful for me.
I would like to build an 8 bit computer and picked ...
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7
votes
1
answer
477
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PDP 11/70: how does MTPI work?
I'm trying to understand the MTPI (and its MFPI counterpart) instruction on the PDP/11.
As far as I understood, it:
it retrieves a value from the "current" memory space with the current ...
22
votes
3
answers
6k
views
Why are these DOS console drivers wasting precious bytes?
While doing some research on DOS device drivers, I took a peek at the console drivers DISPLAY.SYS and ANSI.SYS that are part of the DOS 6.20 installation. Both have "Microsoft" stamped on, ...
- 1,043
0
votes
1
answer
270
views
getting PDP-11 DL11 output via telnet
I'm trying to run the (a slightly adapted version but the original gives the same problem) example program from How to implement a 'write' function in pdp-11 / MACRO-11 / ODT using simh? in ...
7
votes
2
answers
727
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Any recommendations for a Hitachi HD6303 assembler?
Does anyone have any good recommendations for a Hitachi HD6303 assembler?
I've been working on a project to reverse-engineer an executable made for a Hitachi HD63B03 processor. I've finished the first ...
- 836
64
votes
1
answer
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How did the SNES do the “pixelate” transition effect?
This effect is seen in many SNES games, including Super Mario World. The effect pixelates the screen, and makes the pixels larger, then smaller again when it switches to another scene.
It is done so ...
41
votes
12
answers
8k
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When did assembly source code begin to be written in lowercase?
In nearly all the assembly source files and published listings I read up to the early 1980s, the labels, mnemonics, and operands were written in all uppercase. Just a few years later, I noticed 80x86 ...
- 1,313
5
votes
1
answer
495
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Z80 CPU and nested/reentrant NMI
According to multiple documentation sources, non-maskable interrupts (NMIs) can be nested (or reentrant) in a Z80 microprocessor.
This is, upon a /NMI signal pulse, the CPU will interrupt the current ...
- 51
2
votes
1
answer
240
views
Timer B Interrupt occurs only once
I was following this tutorial on Commodore 64 timer interrupts and tried to replicate it (except all I was planning on doing was changing the border color.) I noticed that my interrupt only occurs ...
- 1,638
1
vote
1
answer
263
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Game assembled using RGBDS can't access cartridge RAM
Any writes I do to cartridge RAM on my test game assembled with RGBDS are silently ignored. I wanted to move the stack pointer to cartridge RAM to have more room in high ram to use as a scratchpad, ...
- 1,638
1
vote
1
answer
315
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How does RETN return from NMI on the Z80 in the event of nested NMI?
I was trying to learn how the Sega Master System works. The NMI occurs when the pause button on the console is pressed. So I wrote an NMI handler that makes a beep when the NMI occurs, then waits for ...
- 1,638