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# Retrocomputing : Recent Questions and Answers

## Commercial C64 software implemented in Forth?

There has been several implementations of Forth that were running on, and targeting, the C64. Were there any commercial software releases (not throw-away hobby projects or...

## Execution time for conditional jumps on the Intel 8080

On the Intel 8080, all conditional instructions have varying execution time depending on whether the condition is true or not, except conditional jumps. Why is this? The Intel 8085 changes...

## C64 cartridge emulation with ATmega

As a personal project I had the idea to create a custom cartridge for my Commodore 64 and use an ATmega 1284p microcontroller to emulate eproms and/or custom chips. Basically...

## How does DMACON/R registers on Commodore Amiga platform work?

I have a specific question about the DMACON/R registers found in Commodore Amiga range of computers.As you may know they are the DMA control registers that controls all the...

Asked on 12/25/2021 by Marko L

## DRAW instruction timing

I asked a question here about CHIP-8 instruction timing, and this answer mentions that DRAW waits for vblank:For Chip-8 code that draws anything, the limiting factor will be the...

## Were any M68000 systems capable of generating a "spurious interrupt"?

When an interrupt occurs on a Motorola 68000-family processor, it enters an interrupt acknowledge state, which continues until one of three signals are asserted:An external device places the...

## Change color of the text written in PPU memory (NES-Super Mario Bros)

Let's say I want to write K to the top of the status bar in SMB. I can use the following set of statements to write to PPU memory....

## Which computers had redefinable character sets?

My first computer was an Exidy Sorcerer, bought in the late '70s. It featured a full keyboard including lower case, on screen text of 64 B&W characters...

I was hoping, that someone could help me find the name of the operating system that was originally (I guess) used on the 80286 (the later ones with 12MHz). Before...

## Did OSes write the floppy's logical sector number resulting from sector interleave/skew in the IDAM sector ID, or was it up to the OS?

I've been looking at MicroBee floppy disk image files. They use the DSK/EDSK image file format originally created for Amstrad CPC emulators, probably because both systems use...