Questions tagged [assembly]
For questions about Assembly Language in general. Also use the appropriate processor's tag.
121
questions
5
votes
2answers
241 views
Commodore Plus/4 jiffy clock tied to screen refresh frequency? (warning: flashing images)
Warning: There are flashing images below, do not scroll down if you are sensitive to them!
According to various sources (for example this for the Plus/4), both the C64 and Plus/4 have a "jiffy&...
0
votes
1answer
134 views
Working on programming a retro z80 computer (SDCC error)
I am working on coding a driver of sorts for a Z80 based computer I am making. I am compiling with SDCC and I have been getting the following?
ASlink-Warning-Undefined Global 'data' referenced by ...
1
vote
0answers
103 views
Help debugging a circuit/code for Z80 and TMS9918ANL
I am working on designing a Z80 computer that utilized the TMS9918ANL for graphics. I am currently just trying to make sure the TMS9918ANL is working, so I hooked up the control pins the bus (...
10
votes
2answers
560 views
Trying to understand some assembly syntax in the Unix v7 write system call
so here is the code: (which comes from here, I've also verified this source is in my unix v7 distribution). For reference, this is running on a PDP-11 simulated with the simh program (so please keep ...
4
votes
1answer
470 views
Z80 PIO Keyboard
I am working on designing a Z80 computer and I would like to use a PS/2 Keyboard for input. I would like to use a PIO to communicate with it, but I am having trouble finding any documentation online ...
2
votes
1answer
204 views
How to implement a 'write' function in pdp-11 / MACRO-11 / ODT using simh?
So, I'm working on a project where I'm aiming to get the first winner of the IOCCC (obfuscated c code contest) dissected down to the last detail... The program is mullender.c which you can find by ...
1
vote
1answer
194 views
Using Bresenham's circle algorithm (or another alternative algorithm) to draw an arc [closed]
I'm trying to create some graphics function for a ZX Spectrum (Z80) machine in assembler. I already have the basics except for the arc.
I know that there must be some way to draw an arc using the ...
7
votes
1answer
517 views
On the LR35902, what does the assembly 'LD (HL-),A' do?
I'm working on implementing the instructions of the z80 chip inside a gameboy for an emulator. I'm starting with the instructions in the boot rom that sets everything up.
I've implemented the first 3 ...
34
votes
8answers
7k views
When and why did high-level language compilers start targeting assembly language rather than machine code?
From what I've read, the first FORTRAN compiler built a machine-code program entirely in memory; it was, in fact, designed to read the entire source code of the program, and then sequentially load ...
9
votes
2answers
437 views
How do I tell vasm to allow white spaces?
I have recently been learning to use vasm. For those that don't know, vasm is a cross-platform assembler for multiple types of processors such as the M68000.
http://sun.hasenbraten.de/vasm/
I am ...
11
votes
3answers
324 views
Do any 6502 assemblers have better support for self-modifying code?
I find I keep on doing things like this:
raster_interrupt:
bgnd_color = * + 1
lda #$00
sta $d021
; rest of interrupt handler
so that I can do this kind of thing elsewhere in my ...
1
vote
1answer
303 views
Were all NES games 16 kibibytes or less?
While searching on the Internet and Quora, I found disassemblers for Pac-Man, Galaxian, and Super Mario Bros. The thing that puzzled me, was while Super Mario Bros was arguably quite a complex game ...
17
votes
3answers
3k views
Was there any automated unit testing prior to 1972?
Prior to 1972, was there any automated unit-testing? Did any assemblers include a testing a framework?
I can find some academic journals on this topic from the late 70s -- most of which I don't have ...
31
votes
11answers
7k views
What “unusual” syntax assembly languages are/were there?
This question may have the apparent form of a question soliciting a "list" answer, but I'm expecting the list to be very short, so please bear with me.
What "unusual" syntax assembly languages are/...
6
votes
2answers
504 views
What 6800 assembler to use?
Does anyone know of a good, modern Motorola 6800 assembler?
I've used dasm, which I quite like (and it's even actively developed), but it doesn't actually support 6800. It supports 6803, which is ...
11
votes
1answer
280 views
Inverting the carry flag on an M6800
Are there any tricks that can be used to invert the carry flag on the 6800, in as few bytes as possible?
This is the shortest subroutine I've come up with, which is straight forward:
INVC: BCS ...
3
votes
3answers
438 views
How to transfer the address of a data block into zero page using the Merlin 8 assembler on my Apple //e?
I've been fooling around with the Merlin 8 (v2.58) assembler on my Apple IIe and ran into a small snag.
Basically, I would like to load the address of a block of data into a two-byte pair in zero ...
11
votes
2answers
449 views
Best learning path for Apple IIe assembly language [closed]
I have an emulator up and running and access to the asimov ftp site, and I want to learn how to program assembly language on the Apple IIe. What assembler should I use (Merlin? LISA?) and what book or ...
8
votes
3answers
774 views
How can I access/use memory outside of the standard 1 MB address range of MS-DOS?
How do you access more memory (above the 1MB) in DOS if the 640KB of conventional memory are not enough?
I have read a lot about this, but I couldn't figure out how to do this in actual code. Is ...
5
votes
3answers
314 views
Did the Apollo Guidance Computer or other multi-ROM machines subdivide code between ROM chips/modules to facilitate partial updates?
The Apollo Guidance Computer had its code stored in six modules that held 6 kwords of storage each, and the design of each module was such that changing even a single bit after construction would have ...
8
votes
4answers
1k views
Imaging a HDD from DOS over Serial
I have recently fixed an old IBM Clone, which has an MFM hard drive. The PC booted up fine, but then I saw, that a few years back, I have deleted a few important files (probably by mistake). The ...
1
vote
5answers
915 views
How binaries are generated using Punched cards? [duplicate]
I thought that punched cards already represent the code in binary since a hole means 0 and rest positions mean 1 on a punched card. But then I read that you could use punched cards to present the ...
0
votes
2answers
145 views
RTC 16bit I/O read/write
Why can't RTC (0x70, 0x71) read and write 16 bits? such as
Mov ax, 0xa8f
Out 0x70, ax
But I found in a 286 BIOS that they did this:
(BIOS ID stringļ¼ S286-6181-101590-K0)
00005357 B87253 ...
54
votes
7answers
9k views
Why did the MS-DOS API choose software interrupts for its interface?
Access to the DOS API was done through the INT 21h x86 instruction. This was always counter-intuitive to me, coming from 8-bit systems that accessed system services by calling subroutines through a ...
10
votes
2answers
742 views
Zilog Z80 estimated time discrepancy
I am writing a basic Zilog Z80 assembly language interpreter and something I noticed as I went through the 8 bit load commands is that the estimated times for LD (IX+d), n and LD (IY+d), n are ...
16
votes
12answers
6k views
How can a Z80 assembly program find out its own memory address?
I'm wondering how to write a program in Z80 assembler that discovers its own memory location.
I thought that maybe I could somehow load the program counter PC into, for example, BC.
Is there a way ...
4
votes
3answers
163 views
ca65 vs tass syntax: converting a hex address to decimal?
Most of the tass example programs start with a header like this, which places BASIC code at the beginning of the file that has an appropriate SYS instruction to run the rest of the application:
* ...
4
votes
2answers
706 views
Adding a register to the accumulator in 6502
In the past, the only assembly programming I've done has been a tiny bit of ARM, and then a larger game project in 68k.
In 68k I was used to being able to do things like add.l d0, d1 to add the ...
6
votes
1answer
297 views
Putting code into two different memory areas with cc65/ca65
According to cc65 / ca65 documentation, the .org directive does not affect the placement of the code unlike with other 6502 assemblers. The docs suggest defining a memory segment with the intended ...
2
votes
1answer
144 views
In vasm 1.7d targeting 68000, how to assemble with program counter at specific address without padding?
I'm programming for the Sega Mega Drive using vasm 1.7d assembler. I'm copying a block of my code from ROM to RAM so I can do some self-modifying code.
; First $200 bytes are header, dc.b ...
22
votes
2answers
2k views
Why didn't the 6502 have increase/decrease opcodes for A?
In 6502 Assembly, we can use INX and INY to increase the value stored in X and Y. They can be decreased with DEX and DEY. However, it seems that there are no such instructions for A, like INA or DEA. ...
12
votes
5answers
921 views
Has there ever been a instruction set architecture that did not require instruction decoding at all?
I am studying basic principles of instruction set architectures and am considering what it would take to not have any instruction decoding at all. I.e., all the control lines of the computer would be ...
70
votes
9answers
9k views
Why is the processor instruction called “move”, not “copy”?
Many processors have an instruction called "move" (sometimes spelled MOV) which copies data from one location (the "source") to another (the "destination") in registers and/or memory. It does not do ...
19
votes
4answers
3k views
Why are branches relative in many 8-bit CPUs?
I was looking over an old article on the 6809 and was perusing the opcodes and noticed that the branch instructions came in two flavors, long and short. That sparked a memory about one of the 6502-...
13
votes
3answers
1k views
Memory models for assembly libraries for Turbo C
Turbo C follows the Intel Memory Model where in Tiny, Small and Compact models calling a function is near but in Medium, Large and Huge models calling a function uses far calls.
If I want to develop ...
4
votes
0answers
107 views
MICRO 800 assembler?
I'm reading (well, writing...) about the FLOW language and it mentions the "MICRO 800 assembler". This was in the early 1970s, and I can't imagine what this might be. The context suggests it was on ...
5
votes
1answer
296 views
Adding control characters to string constants in ca65 assembler
According to the cc65 documentation, a string constant in assembler programs can be defined with the .ASCIIZ command. However, I could not manage to sneak control commands in, for example, the ...
6
votes
1answer
205 views
Different handling of ASCII interpretation between ca65 and cl65
I stumbled upon a divergence in the ASCII upper case/lower case handling when using assembler and linker of the cc65 suite separately (I used cc65 V2.15 on Win10).
For a test I made the following ...
5
votes
1answer
292 views
How can I change the MSX function keys using ASM?
How can I change the texts assigned to MSX function keys using Z80 ASM?
15
votes
6answers
5k views
How slow was the 6502 BASIC compared to Assembly
Imagine a modern computer, where let's say Python is a high level programming language and needs to be interpreted in order to execute a piece of code. You could write some code in C, compile it, ...
19
votes
3answers
3k views
What makes MOVEQ quicker than a normal MOVE in 68000 assembly?
I'm "re-learning" 68000 assembly language and came across the "MOVEQ" command that is labeled "MOVE QUICK".
According to the NXP Programmers Reference Manual (reference below), the command MOVEQ (...
29
votes
9answers
10k views
How did early x86 BIOS programmers manage to program full blown TUIs given very few bytes of ROM/EPROM?
I've always wondered how so much functionality and relative luxuries(CMOS Configuration Utilities. See: https://geekprank.com/bios/ for an example) included with most popular x86 BIOSes could be ...
8
votes
1answer
223 views
Are there any PDP-8 assemblers that create linkable object files?
I am currently writing a compiler for the PDP-8. The compiler is going to translate source code into PDP-8 assembly code that calls some runtime routines to perform high-level functions such as ...
5
votes
1answer
576 views
What can an 8086 CPU do if an x87 floating-point coprocessor is attached to it? [duplicate]
As far as I know, old x86 CPUs (for example: the 8086 CPU) couldn't do floating point arithmetic, and in order to be able to do floating-point arithmetic, an x87 floating-point coprocessor should be ...
8
votes
1answer
439 views
What's the fastest way to ignore keypresses?
I'm writing a game for the IBM PC (running MS-DOS), complete with fancy cutscenes. Unfortunately, though, the keys pressed during those fancy cutscenes are carried out once the fancy cutscene has ...
5
votes
5answers
645 views
Did any assemblers work like this?
Once you get past the stage of manually entering numeric machine code, the most primitive programming tool is a machine code monitor. Intended primarily as a debugging tool, this works with a target ...
4
votes
3answers
483 views
Z80 unexpected output
I am trying to build a Z80 computer inspired by Grant Searle's design. I'm starting simple, with just a clock (clocked by an AVR pulsing at at 12.5 Hz for testing), a Z80, and a 8K EEPROM with a ...
9
votes
1answer
818 views
Looking for a specific 6502 Assembler
I found some 6502 assembler code for a Commodore 64 program that uses meta commands like #include "foobar", define the address to be assembled to via *=$1234 and define labels without a colon. ...
10
votes
3answers
1k views
Comparing Signed Numbers on Z80 (8080) in Assembly
How do you compare two signed numbers in Z80 assembly? According to this site,
To compare stuff, simply do a CP, and if the zero flag is set [then]
the argument[s] were equal, else if the carry ...
6
votes
1answer
506 views
Common practices of programming the AY-3-8910 on Amstrad CPC: via Firmware routines or directly?
I'm starting to learn how to program in assembly (z80) on the Amstrad CPC
computer. As an high level developper i find it pretty fun and i learn a lot of
things about computer and CPU architecture.
...
