Retrocomputing newsletter

Top new questions this week:

Why would a NES game use an undocumented 1-byte or 2-byte NOP in production?

Reading the NESdev wiki page on CPU unofficial opcodes, I see a few games use an undocumented 2-byte NOP instuction in production: Puzznic, F-117A Stealth Fighter, and Infiltrator use $89 #i. Beauty ...

programming nes assembly 6502 software-development

asked by JAL 62 votes answered by LOIS 16192 85 votes

What algorithm did Microsoft use to dither colour in early versions of Windows?

In the late 1980s to mid 1990s, most consumer-class video hardware was not capable of displaying greater than 16 colours at a time. To create the illusion of greater colour, software often "blended" ...

windows31 dithering

asked by Mike Nielsen 60 votes answered by phyrfox 68 votes

Can a PET 2001 be physically damaged from BASIC?

In the early 1980s my primary school was the proud owner of a Commodore PET 2001. There was a commonly held belief among the young geek fraternity that there existed a BASIC command—perhaps a ...

basic commodore-pet

asked by Flup 25 votes answered by Kevin Duggan 43 votes

How were Western computer chips reverse-engineered in Soviet Russia?

The British ZX Spectrum computer had many clones in the Eastern Bloc. It seems many of them were built using Russian-made chips from the Angstrem factory in Zelenograd in/near Moscow. The Russian ...

zx-spectrum z80 reverse-engineering

asked by Wilson 20 votes answered by Algimantas 12 votes

How can I create a split-scroll effect in an NES game?

Games like Super Mario Bros. and Super Mario Bros. 3 were able to scroll the playfield but not the status bar: The status bars are clearly too big to be sprites, yet they don't scroll with the ...

nes graphics software-development

asked by NobodyNada 10 votes answered by NobodyNada 10 votes

MSX Assembly/Basic programming documentation

I'd like to try to create software (and maybe simple games) for the MSX standard. I know I have two ways to do so, either I use MSX Basic or Z80 assembly. I think that Z80 assembly is more powerful ...

programming assembly basic msx

asked by user2109 9 votes answered by Konamiman 4 votes

Restore original ROM on PalmOne m515

I've recently bought an old Palm m515 PDA. It seems that the previous owner has removed some of the built-in applications like Calendar and Contacts from it, because when I want to start them it says ...

rom palm pda

asked by gklka 7 votes answered by Stephen Kitt 7 votes

Greatest hits from previous weeks:

What is a use case for the JAM instruction on the MOS Technology 650x family of processors?

I was reading about undocumented opcodes for the 650x family of processors and discovered JAM, an instruction "which simply causes the CPU to freeze, requiring a hardware reset or power cycle to ...

mos-650x

asked by JAL 10 votes answered by Mark 25 votes

Where can I find an external 8-inch floppy disk drive?

Where can I find an external 8-inch floppy disk drive? I have some data I would like to retrieve from a really old 8-inch (200 mm) floppy disk, but have no working computer than has a drive to read ...

floppy-disk disk-drive

asked by Jeff 9 votes answered by Stephen Kitt 12 votes

Can you answer this?

R.O.B can't move up or down

I got this R.O.B, first time I turned him on his arms wouldn't close, so I took him apart and cleaned him. I put the gears back into place. After turning him on again and testing him he won't move up ...

nes repair

asked by Justin 1 vote