Questions tagged [6502]
For 6502 series of processors, including hardware and assembly language questions. Use with [hardware] for the hardware interface in particular.
204 questions
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Way to implement multi threading on a MOS 6502 type CPU [closed]
I'm trying to write an OS for the W65C02 CPU but i'm stuck because I have no idea on how to implement concurrency on such old CPU.
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How to address MEGA65 memory above 64 KB in VBCC?
Could you please help me to address MEGA65 memory above 64 KB using VBCC compiler?
Below example of changing color attribute of a character works just for memory below 16-bit address space:
#define ...
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Did any notable 6502 systems coordinate DMA with start of instruction rather than adding delay for possible writes?
An annoying hardware quirk of the 6502 is that while the READY line can be used to extend read operations, it cannot be used likewise for writes. As a result, systems which need to accommodate DMA ...
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"Paul's method" moniker for the 6502 RTS trick
In 6502 assembly programming, there's a common trick (usually called the RTS trick) for performing indirect jumps by pushing the target address minus one on the stack and executing a RTS instruction. ...
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How can a dummy learn assembler? (IIgs) [closed]
I would like to write some interesting programs in assembler but I don't know where to start and how to do it. I would like a guide in simple language for dummies. Does anyone have a list of such ...
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Manual for the Microtec 6502 assembler?
The Atari OS, and I suspect other "major" programs from that era, was written using the Microtec cross-assembler. I have found manuals for the Intel version as well as their later 68k ...
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How does one modify a 6502 board to use a 6802?
The Apple 1 was designed to be able to use a 6800 as well as a 6502, with PCB circuits to add the required clock generator and jumpers to accommodate the slightly different pinout. (The design had ...
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Why can't I read this EEPROM
I'm refurbing an old 1980 UK101 Computer. It has a monitor (CEGMON) programmed into a 2K EEPROM, which is unmarked. However looking at the wiring, and the other ROMS in the machine, it's a 2716.
I ...
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Assembler/disassembler/etc to convert 6502 code to 65C02?
I'm wondering if anyone has ever come across a cross-assembler that takes 6502 code, in machine or assembler form, and converts it to use the new instructions available in the 65C02, or even the ...
- 22.4k
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Why does Burger Time ROM contain EOR and ROR instructions that don’t actually execute as such?
I disassembled Burger Time (Data East set 1) arcade game from MAME as I always do when I want to reverse engineer a game.
This is a 6502 processor, which I know pretty well as I coded & reversed a ...
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Why does Super Mario Bros (NES) preemptively clear the hidden 1UP flag before Mario hits the block?
I'm analyzing the disassembled code of Super Mario Bros. (NES) and came across some logic related to hidden 1UP mushrooms. While debugging the game alongside the code, I noticed something unexpected: ...
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Fastest quasi-random function in 6502?
I am hacking around with the Oric Atmos computer, and it has an interesting video display scheme, involving attribute values which change the behaviour (ink/paper colours, blinking, invert) according ...
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Removing Graphics, but not Sprites on C64
I am trying to remember that removing all graphic elements, but not sprites. The aim is to disable DMA and ease to open side borders etc...
As I remember it was an option at $D011, but it seems it ...
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How to insert custom code into Super Mario Bros. NES file
I have a hobby project requiring adding some code to Super Mario Bros NES file.
Specifically I want to display custom text (at least 22 letters and numbers, but more likely above 100 characters) after ...
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Apple IIe Enhanced not following BEQ correctly
I'm running the example code from Assembly Lines chapter 5 programs 2A and 2B which print the entire character map for the Apple II and then are supposed to break, however my code is looping ...
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