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Note:  All links are to the 6502, HP-41, and related things.  Please do not ask me to add a link to your stop-smoking program or anything else unrelated to my website.

Major features on this website: (and other major features are planned, plus several smaller ones, but it all takes so much time!)

list of 88 of just my own articles, on this site and others

Link categories on this page:

65-family processors, history, HDL, emulators (which are hardware):

Why use the 6502? (2-page forum topic, with links to more)  It has great strengths that don't initially meet the eye!
6502 origins
65816 origins, 6516, 65032, 65832
65CE02 improvements over the 65c02  Original Commodore 65CE02 data sheet is here (.pdf)  See also the many links Ed Spittles provides regarding the reverse-engineering and high-resolution die images of the 65CE02 in the forum topic "Notes on reverse-engineering the 65ce02"
6516 (Synertek) 16-bit pseudo-6502 for Atari 400/800 computers, never made it to market
HuC6280, a PC Engine using a special version of the 65c02 (with all the modern CMOS instructions minus STP and WAI), with a memory management unit (MMU).  Of special interest are the instructions directly involved with memory mapping and moving, and a T flag, which when set (using SET), causes accumulator instructions to operate on the ZP address pointed to by X instead, without affecting A!  It makes it like having 257 accumulators.
65020 double-wide 6502 proposal
6502EX (6502 extended to 32 bits)
65E4, from MOS Technology (.pdf)  Never made, but intended to be a powerful high-level 32-bit successor to the 6502, and a good compiler target, and run multiple protected processes.  For a brief summary and forum discussion, see the forum topic.
65832, from WDC (.pdf)  Never made, but intended to be a 32-bit successor to the 65816.  Apparently it was designed for Apple to make a 32-bit 65-based homne computer, which never happened.
65Org32 developments of ideas for an all-32-bit 65816 extension (forum topic)
65GZ032, a 6502-compatible 32-bit VHDL core from Gideon Zweijtzer and his team.  They had hardware working, but never finished.
65m32, a 65-oriented 32-bit processor concept from Michael Barry.  Operands up to 16 bits wide are merged with op codes so the entire instruction can be fetched in a single clock cycle.
Ed's roundup of links to forum topics on improved 6502 and derived architectures

Silicon Genesis interviews: Bill Mensch, inventor of the 65c02 and 65816 (about 40% of the way down the page)  Click on his name, the title above that paragraph, for the video interview.  If you click on the "here" which is the last word in the paragraph, you'll get the text trascript instead.
Bill Mensch interview Aug 2015 on 6502 and '816, and comparing them to ARM, 68000, x86, 6800, 6501, etc. and his business model, and his goals.  He obviously has a very clear vision, and he's accomplishing what he wants. Still. Today.
David Cramer interview (VP of business dev at WDC) Mar 2015.  He says there are hundreds of different products being made today with 65xx processors in them.
Chuck Peddle gives reasons for design decisions on the 6502

6502 emulation with an ARM
6502 emulation with an AVR by Daryl Rictor
6502 emulation with an ATMega16 by Klaus Dormann  (See also this forum topic.)

Daryl Rictor's 65802 module, a hybrid using a 65816 and other ICs to plug into a 6502 socket like WDC's no-longer-available 65802.  The forum topic that goes with it is here.
A2Heaven's 65816-to-6502 converter module, which seems to be the same thing as Daryl's 65802 module above

How 6502 illegal op codes really work
More on illegal op codes
Yet more on illegal op codes
x7 and xF illegal op codes article from Byte magazine, Dec '77
visual6502 wiki page on illegal op codes
No More Secrets v0.9 [2015] A very complete, 67-page indexed .pdf illegal op code reference, very nicely laid out, with good explanations of every instrucion.  From The C-64 Scene Database.

Rob Finch's bc6502 verilog 6502 source  (Note: This finitron website is his newer one, but the file dates are older than what's in the archive.org URL linked in the 65xx HDL page linked above.)
links to 18 free HDL 65xx cores
comparison of many HDL 6502 cores available (forum topic, with links)
BMOW tiny 6502-like CPU in CPLD
programmable-logic basics: free online course
links to more help understanding the innards of the 6502 at the gate and transistor level
For 65-family peripherals made with programmable logic, see the next section below, "65-family peripheral ICs."

KimKlone 65c02 with pointer-arithmetic-friendly extended address space and 9-cycle ITC Forth NEXT, by Jeff Laughton
Build your own 6502 with TTL by Ruud Baltissen
6502 ALU using 74xx logic (minus BCD), by someone called "latebit"

Western Design Center (WDC) is the main 65c02/816/134/265 manufacturer today.  See also http://wdc65xx.com/ which is another site of WDC's.  Data sheets for currect production can be found at http://wdc65xx.com/support/documentation/.
Jeff Laughton's improved to-scale timing diagrams for 14MHz 65816, including for understanding to help prevent bus contention at changes in data direction which can happen twice per '816 clock cycle.
Jeff Laughton's animated visualizations of timing margins  These excellent, drawn-to-scale (unlike most in data sheets) .gif's help understand what timings are constant and what varies with clock speed.  Discussion about them is in the forum topic here

65-family peripheral ICs:

my "Tip of the Day" column for 6502 development has many tips on using the 6522 VIA and 6551 ACIA
Daryl Rictor's 65SPI IC he sells.  It is a 65-family I/O IC to multiple SPI devices.  Note, 10/24/18: The CPLD Daryl was using to make the 65SPI was discontinued.  If you want a 65SPI and he's out, I have some here I can part with.  He is working on transitioning the design to a newer CPLD.
6581 SID emulator in Atmega8
SwinSID 6581 emulator in 32-bit ARM Cortex running at 80MHz  (There are different versions there.)
SwinSID Ultimate SID Chip substitute for Commodore 64, from "The 8-Bit Guy"
Papilio Duo C64SID SID in FPGA
6502.org's datasheet index
data sheets to lots of less-common 65-family peripheral ICs (Rich Cini's site)  In fact, there he has hundreds of scanned Apple, Commodore/MOS, Synertek, Rockwell, and other books and documents.
Western Design Center (WDC) is the main 65c21/22/51 manufacturer today.
Jeff Laughton's unconventional circuit tricks for ultra-fast (single-cycle!) I/O using 65c02 illegal op codes in the _3 and _B columns, plus re-mapping op codes  (This is in the circuit potpourri page of my 6502 primer.)

interfaces and buses (also see the descriptions on en.wikipedia.org):

digital audio plug-in modules for Commodore 64/128
Wishbone computer bus
concise comparison of synchronous-serial interface types (forum post)
I2C overview from Philips Semiconductor (.pdf)
I2CChip.com I2C, SPI, 1-Wire interfacing made easy
guide to reliable 1-Wire® networks
Microwire/Plus description from National Semi (.pdf)
B&B Electronics: serial converters
65SIB spec. (serial interface bus, hobbyist-friendly, compatible with SPI, Microwire, and dumb shift registers, but more flexible)
SS22 spec. (6522 synchronous-serial data link between computers)
I2C-6: proposed connector standard for I²C, hobbyist-friendly, suitable for breadboarding (6502.org forum)
SPI-10: proposed hobbyist-friendly connector standard for small SPI modules, suitable for common perfboard
My RS-232 primer
SD-card SPI Maxim ap note (.pdf)
SD/MMC cards, using in SPI mode
SD/MMC/SDHC card library
USB/Bluetooth for Apple II
USB modules (Hobby Engineering)  Note, fall 2016: (hopefully) temporarily closed due to a bad accident.
MAX3421E USB peripheral/host controller IC with SPI
running the bus off the board, and interfacing external boards and devices (forum posts)

65 software: math (including coprocessors), algorithms, simulators, OSs, programming languages, programmers' info:

    (See also the assemblers and Forth sections further down)
Large look-up tables for super fast, accurate, 16-Bit scaled-integer math (like having a coprocessor)
6502.org wiki (math, utility routines, datasheet errata, etc.)
source code on 6502.org, in various categories
tutorials and primers on 6502.org
Nesdev wiki programming guide index
Self-modifying code on 65xx
Omegamatrix's fast, short division routines to divide an 8-bit number by any number up to 32
Lots of 6502 books, including for programming, scanned and available for download.  See especially under "Programming", starting about 70% of the way down the page and going to the end.  I have a few of those in paper.
Taygeta C64 Forths
Forth processors (stack computers)
EhBASIC by Lee Davison.  An outstanding interpreted BASIC for 6502.  Note: If that link doesn't work, try this one.  Unfortunately Lee passed away, in 2013.  Bruce Clark has documented 11 EhBASIC 2.2 bugs in the forum topic EhBASIC 2.2 bugs. Then, although the following is not a bug, he discusses it in the forum topic Exponentiation with integer exponent to be aware of.  The EhBASIC section of the 6502.org forum is here.  Hans Otten has had some success is reconstructing Lee's website, here.
Create your own version of MS BASIC for 6502
Microsoft BASIC for 6502 Original Source Code (1978)
Steve Wozniak's Sweet16, a memory-efficient, 16-bit virtual machine implemented in 300 bytes of 6502 assembly language, originally for Apple II
cc65 wiki.  cc65 is a 6502 C compiler and supporting software.
The cc65 C compiler and assembler home page
high-speed function approximator using Minimax quadratic interpolator
HAKMEM programming tricks (math, algorithms)
many math routines in 6502 assembly on the Codebase 64 wiki
Codebase 64: Commodore 64 source code, articles, tutorials
CORDIC algorithms for FPGA-based computers (.pdf)  (this link has the same article)

André Fachat's context Switching and thread synchronization on a 6502
André Fachat's GeckOS/A65 V2.0, a full-featured Multitasking/Multithreading OS for the 6502.  It is preemptive and implements some Unix-like features, like signals, semaphores, relocatable file format, standard library, internet support via simplified sockets, and virtual consoles.
Jonathan Halliday's preemptive multitasking GUI OS for Atari 6502 computers
DOS/65 CP/M-like OS for 6502
operating-system wiki (OSDev.org)
6502.org forum topics on OSs:
    CP/M-65 or DOS-65
    BIOS for the 65C816?
    Just an idea: a CP/M alike OS for the 6502?
    Microtan 65 DOS ROM (only one post)
    '816 OS thoughts
    introducing minimOS
    C02Monitor and C02BIOS
    OS dev
    Apple ProDOS 1.7 source - updated to ca65. Kinda compiles...
    Attempting to code a password secure OS.
    Colonel -- A Commodore OS Expansion Research Project

IEEE floating-point standard (.pdf)
IEEE-754 floating-point standard for arithmetic (Wikipedia)
IEEE floating-point conversion page
6502 BCD floating-point scientific math package, 12-digit plus 3-digit exp, up to hyperbolic functions
128-bit floating-point 65816 implementation, up to log, trig, and hyperbolic functions, by Marco Granati  (Note, Sep 1, 2018:  I see the link has gone dead.  Until I get an updated link, use the archived page at https://web.archive.org/web/20170304155404/http://65xx.unet.bz/fpu.txt or https://web.archive.org/web/20170923012704/http://65xx.unet.bz:80/fpu.txt
AWC Electronics math coprocessors, 32-bit floating-point, serial-interfaced
Micromega Corporation math coprocessors, 32- and 64-bit floating-point, serial-interfaced

sorting algorithms, as dances
BDD's 65816 string-manipulation library
BDD's Supermon 816 machine-language monitor for the 65816  (Also at this forum topic.)
list of free 6502 monitors, on the mos6502 g+ group
Program-Writing: Where Do I Start?     (section 18 of the 6502 primer)
Tips For Programming the 65(c)02 (sometimes affecting hardware design optimization)    (section 20 of the 6502 primer)
my program structures in 65c02 assembly, through macros (for PIC16 also)
simple methods for multitasking without a multitasking OS, for systems that lack the resources for a multitasking OS, or where hard realtime requirements would rule one out anyway
programmers' articles about memory
6502 v. 65816 code length comparison
6502 v. PIC16 code length comparisons
"Programming the 65816—Including the 6502, 65C02 and 65802" 6502/65816 programmer's manual by David Eyes and Ron Lichty.  This is definitely the best 65xx programming manual available, and a must-have for every 65xx programmer!  It starts with the basics, followed by architecture, the CMOS 65c02's many improvements over the original NMOS 6502 including added instructions and addressing modes and fixing the NMOS's bugs and quirks, and then the natural progression to the 65816; a thorough tutorial, writing applications, then very detailed and diagrammed information on all 34 addressing modes, at least a page of very detailed description for each instruction, with info on every addressing mode available for that instruction, then instruction lists, tables, and groups, of all 255 active op codes, plus more.  469 pages.  From Western Design Center.  (.pdf)  Note: There were many problems with the earlier .pdf version that were not in the original paper manual; but in late March 2015, WDC scanned and OCR'ed the paper manual and posted the new, repaired .pdf.

uIP TCP/IP stack for 6502 (lots of search-engine results)


Western Design Center's (WDC's) sofware tools  WDC is the 65c02 and 65816 intellectual-property owner.  Download is free.
65816 free assemblers
lots of 6502/816 assemblers, disassemblers, C compilers, simulators, & related tools
Andrew Jacobs' As65 assembler which has program-structure capability built in
Anton Treuenfels' HXA 6502 assembler which also has program-structure capability built in
P65 portable 6502 assembler
64tass powerful macro assembler and linker for 6502, 65C02, R65C02, W65C02, 65CE02, 65816, DTV, & 65EL02, from soci
Cross-32 (C32) assembler (which I use) formerly from Universal Cross Assemblers, now sold by Data Sync Engineering.  Also available at http://www.mpeforth.com/cross32.htm.
asmx is another multi-CPU macro assembler.  It's free, but apparently does not quite have full 65816 support like C32 (above) does.
Merlin 32 modern cross-assembler, linker, disassembler, simulator, and more, for 6502, 65c02, 65816, for Apple IIgs and others, by Antoine Vignau and Olivier Zardini
SB-Assembler 3 (free) which now runs on Linux, MAC and Windows machines, and assembles for 6502, 65c02, and many other microprocessors and microcontrollers, announced Dec 7, 2016.  There are also earlier versions available that run on DOS and Apple II and even Apple I.
MADS multi-pass crossassembler for 6502 and 65816.  (This page is mostly in Polish, but important stuff is available in English through the links in the top-right corner.)  Binaries are generated mainly for Atari 8-bit systems (supported are AtariDosII and SpartaDOS X formats).
Assemblers And Loaders 1993 book by David Salomon on how to write them.  294 pages.  Available for free download.   (Not 6502-specific.)
Michal Kowalski's 6502 IDE and simualator (.zip download, with executable for DOS/Windows, but can be used with Mac & Linux under WINE)  More info here.  It's all on github too.
BDD's macros for assembling 65816 code on Kowalski's 6502 assembler
Kick Assembler for NMOS 6502 is the main (but not the only) one discussed in the Retro Assembler facebook group, at the link.  It is written and well maintained by Mads Nielsen on that page.  You can have direct contact with him there and get quick answers.  You can download the Kick Assembler here.
6502 disassemblers written in BASIC (several, in a forum topic)
NESHLA: The High Level, Open Source, 6502 Assembler for the Nintendo Entertainment System
Coldfire macro assembler, simulator, and debugger for 6502/65c02

for individual computer brands:

Acorn BBC Micro (Beeb):
Acorn BBC Micro (beeb)  Lots of links to beeb resources (forum post)

AIM-65 and Rockwell R6500 scanned manuals, books, diagrams, magazines, ROM images, etc. on Rich Cini's site.  About 80 files, and some .zip files may have more.
Interactive (a newsletter published by Rockwell International.  It featured articles by Rockwell employees and individual contributors, focused on the AIM 65 single board computer and related Rockwell products.  Scanned issues, on 6502.org)

Apple II:
GGLabs sells their RAMGS/8 small form factor 8MB memory expansion for the Apple IIgs (introduced in May 2018), and other modern hardware and software products for Apple II
Apple II original ROM info, ROM listing, Sweet 16, monitor, floating point, articles, plus SYM and AIM monitors, and AIM BASIC ref manual.  257 pages.
eBook: "What's Where in the Apple" 400-page Apple II resource which had been out of print since '84
SD card "drive" for Apple II on Hack-a-Day
Apple IIgs programmers' home
Apple II source code for the LOGO language found
loads and loads of scanned Apple II books
Apple I & II podcasts on Floppy Days Vintage Computing
More than 30 scanned Apple II & IIgs books and documents on Rich Cini's site.
"Apple Assembly Line" archived issues, 1980-88
Assembly Lines: The Complete Book  (.pdf, 458 pages!), by Roger Wagner, pres. & founder of Southwest Data Systems.  Has all 33 articles, including those that never got published in Softalk magazine.  There's more info here, with a 3-minute video from the editor, Chris Torrence.  Quote: "Now, for the first time, all thirty-three articles are available in one complete volume.  This edition also contains all of the appendices from the original book as well as new appendices on the 65C02, zero-page memory usage, and a beginner's guide to using the Merlin Assembler.  The book is designed for students of all ages: the nostalgic programmer enjoying the retro revolution, the newcomer interested in learning low-level assembly coding, or the embedded systems developer using the latest 65C02 chips from Western Design Center."
Call A.P.P.L.E. World's largest Apple users' group, since 1978.  Here's an example of articles there, published 7/5/18: "Tome of Copy Protection released by A.P.P.L.E.  'Copy protection is designed to keep people from making copies of a disk.  Because of the complexity and 'hidden' aspects of copy protection, most people have little or no idea how this protection works.  This 380-page book is designed to help you understand what is going on with your protected Apple II disks, and possibly show you how to copy them, or create your own copy protection scheme.'"

Apple III:
Floppy Days 88 - The Apple III, Part 2 with Paul Hagstrom (page with podcast followed by loads of Apple III links, which I won't repeat here).  Part 1 is here.
Floppy Days 89 - The Apple III - Part 3 with David Fradin

Atari Archives
APE Atari pages
Trevin Beattie's Atari Technical Information page
loads and loads of scanned Atari books
Atari Wiki

GGLabs sells their GRAM/1D 1MB geoRAM clone (introduced in Jan 2018), and other new hardware products for C64 & 128
DLH's Commodore Archive  Tons of Commodore documents
Zimmer's Commodore pages
Source code of GEOS 2.0 for the Commodore 64
The Fridge source code programmers' resources for C64 and 6502
64 Bites C64 programming tutorial videos.  They say it's "The easiest way to start programming Commodore 64," and Michal Taszycki says, "I am working hard to make it the #1 best place to learn about Commodore 64 in the world."  (Although most of the resources in this links page are free, the videos on 65bites.com are not.)
Commodore PET index, and another one here (in the last half of the post, with links to PET documents on 6502.org)
Commodore.ca  All things Commodore
The C-64 Scene Database, dedicated to gathering as much information as possible about the productions, groups, sceners, events, and BBS's in the Commodore 64 scene
Dan's 8-bit Commodore Info  Lots of Commodore links
Commodore disc images on CD  Over 1100 disc images (D64 and ADF) containing over 10,000 programs for C64, VIC20, Amiga, C128, and PET, many of them originals published by TPUG, plus historical photos, emulators, and the library catalogs in PDF format.
Commodore.software, archived software and reference material for most Commodore computer systems.  There are C64 and Pet BASIC compilers here, and lots more Commodore links here.
Commodore 1541 floppy-disc drive ROM disassembly
The C64 PLA Dissected (.pdf)
modern products for C64 from NKC Electronics
V-1541, a virtual 1541 disc drive that you can use from your Commodore 64 computer
Pi1541 a realtime, cycle-exact, Commodore 1541 disc-drive emulator that runs on a Raspberry Pi 3B (or 3B+).  By Steve White.
Commodore Wi-Fi modem
Flyer, the combination internet modem and disc-drive emulator for Commodore 8-bit computers
C64Net WiFi Card adds wireless internet to your Commodore 64 computer.  It supports an AT command set similar to the Hayes smart modem.  It is capable of communication at speeds up to 9600 baud.
C-One FPGA-based enhance adaptation of the Commodore 64
Turbo Chameleon 64 multipurpose cartridge for the Commodore 64 — and a lot more!  There's a demo YouTube video of it here
Codebase 64 wiki C64 source code, articles, tutorials, magazines, books, projects, and links
SuperCPU Home
loads and loads of scanned Commodore 64 & 128 books
loads and loads of scanned manuals for Commodore 64, accessories, and software
lots of scanned Commodore PET books
More than 70 scanned Commodore and MOS (including KIM-1) books and documents on Rich Cini's site.
Retro Innovations Store facebook page for new boards and accessories for VIC-20 and C64
ACE OS by Craig Bruce for the Commodore 128 and 64 that provides a Unix-like command-shell environment.  All ACE programs will run on either a C128 (in 128 mode) or a C64.  "ACE" stands for "Advanced Computing Environment."
C64 OS has one goal: To make a Commodore 64 feel fast and useful in today's modern world.
CBUG Escape (perical published by the Chicago B128 Users Group.  Scanned issues, on 6502.org.)
Northwest Computer News (periodical, published by Bruce Faierson through his company Northwest Music Center of Deerfield, IL, focused on the Commodore B128.  Scanned issues, on 6502.org.)
Commodore Club News (perical published by the UK division of Commodore Business Machines.  Scanned issues, on 6502.org.)
Commodore Computing International (periodical published by Nick Hampshire Publications of the UK.  Scanned issues, on 6502.org.)
Commodore PET Users Club Newsletter (periodical, an official Commodore publication for PET users.  Scanned issues, on 6502.org.)
geoNEWS (periodical, published by the UK-based geoCLUB, this newsletter supported users of GEOS on Commodore computers.  Scanned issues, on 6502.org.)
ICPUG Newsletter (periodical, published by the Independent Commodore Products Group of the UK.  Scanned issues, on 6502.org)
PET Gazette (periodical, published by Len Lindsay of Madison, Wisconsin.  Scanned issues, on 6502.org)
The PET Paper (periodical, published by ARESCO of Audubon, Pennsylvania.  Scanned issues, on 6502.org)
PET User Notes (periodical, publication of the PET User Group focused on early Commodore PET computers.  Scanned issues, on 6502.org)
PET Users Group Newsletter (periodical, published by the University of California at Berkeley's Lawrence Hall of Science under the Computer Project.  Scanned issues, on 6502.org)
SPOT: Society of PET Owners and Trainers (Periodical.  SPOT, the Society of PET Owners and Trainers, covers the early years of the Commodore PET.  SPOT was first published in the People's Computers newsletters and edited by Phyllis Cole.  It was then published in Recreational Computing magazine and edited by Harry Saal, who provided these extracts.  Scanned issues, on 6502.org)
PRINTOUT (a Commodore PET magazine published by PRINTOUT Publications of the UK.  Scanned issues, on 6502.org)
SuperPET Gazette (published by the International SuperPET Users Group (ISPUG).  Scanned issues, on 6502.org)
Mike Naberezny's PET/CBM pages
The Zero Page (publication, user group newsletter published by Commodore Users of Wichita.  Scanned issues, on 6502.org)
Ilker Fiçicilar's Commodore 64/128 projects (partly in Turkish)
Cenbe's Lyon Labs Commodore 64 pages (including a large subsection on GEOS for the C64
Many Commodore treasures on pagetable.com:
6502 User Notes (publication, originally known as KIM-1 User Notes, 6502 user notes, focused on the KIM-1 and related products from MOS Technology.  Scanned issues, on 6502.org)
Memblers' resource-rich NES page
Dave's OSI (Ohio Scientific) pages
loads of documents on AIM-65, Apple II, VIC-20, C64, Kim-1, Sym-1, others  (Rich Cini's site)
Briel Computers retro computer kits: Apple, Altair, KIM, others, plus modern accessory boards
Compute II (publication, a spin-off of the original Compute magazine.  It supported the popular 6502-based single-board computers of the time, particularly the KIM, SYM, AIM, and OSI.  Scanned issues, on 6502.org)
Dr. Dobb's Journal (publication, initially published by the People's Computer Company, this newletter started in 1976 and covered many topics from the early days of hobbyist computing.  When the 6502 appeared, various articles were written in Dr. Dobbs about it, and this is some of the earliest content about the 6502.  Scanned issues, on 6502.org)
MICRO: The 6502 Journal (A publication, MICRO was geared towards all 6502-based systems.  It regularly featured articles for single-board computers such as the KIM-1 and SYM-1, as well as desktop machines of the time such as the Commodore PET and Apple II.  Scanned issues, on 6502.org)
SYM-PHYSIS A publication, SYM-PHYSIS was the bimonthly newsletter of the SYM Users' Group.  It focused on the Synertek Systems products such as the SYM-1 and close relatives.  Scanned issues, on 6502.org)

65-family current suppliers:

Western Design Center (WDC) makes and sells 65-family hardware (all 14MHz+) but makes most of their money licensing IP.
list of distributors

6502-related discussion groups:

6502.org website: many homebuilt projects, primers, tutorials, books, data books, articles, magazines, dev tools, source code, etc.
6502.org forum (lots of activity, unlike the Yahoo forums below)
6502 CPU Family facebook group  (Consider facebook groups to be more of a chat room, since fb records are not very permanent, nor searchable, and they don't allow categories or any formatting options suitable for code or much of anything except chats.)
Atari Age forums
SuperCPU Coding facebook group
Retro Assembler facebook group is dedicated to 6502 assemblers, primarily (but not only) the Kick Assembler.
MOS Technology facebook group
6502 Homebrew Hardware and Programming facebook group
GEOS - Wheels - GeoWorks - MegaPatch - gateWay facebook group
6502 Yahoo forum
Apple II Yahoo forum
C64 Yahoo forum
CSDb C64 forum
Lemon Commodore 64 forum
Denial Commodore VIC-20 forum
NesDev NES development forum
OSIweb (Ohio Scientific) forum
The mos6502 page on G+ ran weekly posts from July 2012 until March 2019, when G+ closed.  Every post is described and linked on the 6502.org forum, in these posts.
See http://6502.org/groups for 6502-related USENET newsgroups and mailing lists.
Vintage Computer Forums, including sections for Apple II, Atari, Commodore, vintage computer programming, etc.

others' 6502 web pages (definitely non-trivial!)

André Fachat, HW & OS architecture including a multitasking, multithreading 6502 OS
Daryl Rictor's 6502/816 boards, modules, and parts he sells
Sprow's MiniB BBC-Micro-based SBC
Douglas Beattie's 6502 pages
excellent visual transistor-level simulation of 6502
BCS Technology, "BigDumbDinosaur's" site, with his POC V1 SBC
Hans Otten's retrocomputing pages, mostly 6502


techniques for construction of reliable high-speed digital circuits (forum topic, with lots of good resources)
wire-wrap Q&A (section 12 of the 6502 primer)
raster graphics on an analog oscilloscope (involving a 6522 VIA's shift register port)
stacking ICs to get more on a board (in the lower third of the page)
VGA primer
my "Tip of the Day" column for 6502 development
my article on interrupts.  6502 has outstanding interrupt performance compared to other processors.  (Enjoy my out-of-date cartoons! :) )  It's also on 6502.org, here.
BDD's 65816 follow-up on my 6502 article on interrupts (also posted on 6502.org, at http://6502.org/tutorials/65c816interrupts.html)
my project pages on 6502.org.  The workbench computer portion is especially outdated, so see the page here instead.  I want to eventually get it all on my own site here, up to date, more complete, and with more pictures and better scans.  I use my workbench computer as kind of a Swiss army knife for the workbench.
many 6502 books and magazine articles for free download
thousands of scanned magazines, C64, Apple, other
thousands of scanned books on 6502, C64, PET, Apple, Atari, others
800+ archived articles on 6502
my slide rules I used in my early years (also slide-rule links)


Software survivalism, by Samuel Falvo  (In spite of the name, it's about hardware too.)  I would like to see this way of thinking become more popular and organized.  (If that link ever goes down, it's cached here on this site, with his permission.)
Neo-Retro Computing, by Samuel Falvo.  (If that link ever goes down, it's cached here on this site, with his permission.)
Low Fat Computing (A politically incorrect essay by Jeff Fox)  He and Chuck Moore (inventor of Forth), taking an entirely different programming philosophy, plus Forth hardware and software, have improved the compactness and speed of code by factors of 100 to 1000.
ANSI Forth is anti-Forth, by Jeff Fox, agreed by Charles Moore, inventor of Forth.  See why.
Assembly Language:  Still Relevant Today
Why I do this web site
Why we do 6502 (forum topic)
Things I do and don't like, relating to the computer hobbyist  (You don't have to agree.)


my 32-bit DO LOOP & related words in 6502 ITC Forth
Taygeta C64 Forths
Forth processors (stack computers)
Stack Computers: The New Wave The entire book is available to read online or to download.
Many links for stack computers and Forth material
UM* (multiplication) bug in common 6502 Forths (and my fix)  Also shows some faster variations, with code size and speed comparisons.
UM/MOD (32-bit division) bug in common 6502 Forths (and my fix)
D< bug in common Forths, plus my fix (on forum)
65c02 interrupt service in high-level Forth, with zero overhead!
KimKlone 65c02 with pointer-arithmetic-friendly extended address space and 9-cycle ITC Forth NEXT, by Jeff Laughton
6502.org forum Forth topic index
Bruce Clark's 2-instruction 65816 NEXT in ITC Forth
Bruce Clark's single-instruction, 6-clock 65816 NEXT in DTC Forth
Bruce Clark explains how the faster-running STC Forth avoids the expected memory penalties.  He gives 9 reasons, starting in the middle of his long post in the middle of the page.  STC of course eliminates the need for NEXT, nest, and unnest, thus improving speed.
"Starting Forth" book by Leo Brodie, available online, somewhat modernized, but with the original cartoons.
explanation of five different Forth threading methods, by Brad Rodriguez.  There's a list of more of his related articles at http://www.bradrodriguez.com/papers/.
Walter Rottenkolber's explanation of the A081 in figForth's 6502 Forth, for forming new vocabularies
Atari Wiki Forth index
linked list of articles in Forth Dimensions magazine on the Forth Interest Group's (FIG's) site, many 6502-related.  See also this page to read entire issues online.
See also the links in the philosophy section above.

HP-41 calculator/computer:

HP Journal, Mar 1980 (pdf), 26 pages of articles telling about the design of the new HP-41c, card reader, HP82143A printer, LCD, and more
Clonix-41 (I have this one, and loaded into it, ROM module images of the Advantage, ZENROM, 41z, Warp_Core, and Library 4)
MLDL2000 and other 41c info, from Meindert Kuipers
MLDL2000 pictures
HP41CL (50 times as fast, 200+ KB of RAM, over 300 modules built in, retains port compatibility) (.pdf)
The IC Monte uses to make the 41CL is going out of production.  See this forum topic.  If you want a 41CL, you better order soon.  It wouldn't surprise me if something else comes online later, possibly better, but it may be a long time.
Newt: 41 processor emulator (for 41CL) (.pdf)
NEWT processor and 41CL
41CL wiki
Vintage Calculator Repair  (Bruce Larrabee's repair service)  A death in the family caused a lot of chaos and stress in the family and made him unable to maintain the calculator repair business for the last year and a half, and neck surgery didn't help the situation either; but an update on his site 4/12/17 says he's back to the repairs and has some improvements in his process that should speed things up.  He has a new phone number, 541-731-5130, which you can call 9:00 am to 8:00 pm PST.  Note that he has moved.
flex-circuit replacement  There's a video showing how to install the replacement here.
3D-printed back cover replacement parts for HP-41  (forum topic, with links)
3D-printed module shells, battery holders, side covers, more options!  also for lithium batteries, HP-IL cable clips, and HP-71 and HP-75 modules and covers!
41cv coconut repair
41 LCD pictures, for servicing
Post replacement that works! (forum post)
For card-reader repair, see here and here.
French HP-41 forum
3E0_RTN's Corner (French)
French HP-41 website
HPIL files explanation
LIF utilities for Linux
LIF file types v8 .xlsx, 10 of them being used by the HP-41
11 extended-memory file types used in the HP-41 (and you thought there were only 3!)
HP82161A HPIL digital cassette drive service manual
HP computer museum (Australia)
HP calculator museum
HP41.org, called TOS (for "that other site") at HP Museum (I am a moderator on the forum
List of collections of calculator related documents MoHPC forum topic with links
The PPC Calculator Archive: A Work in Progress Since 1998 PPC DVD with: ...and more.  The DVD is around $25 including shipping.  The price varies slightly based and whether you're an HPCC member and where you want the DVD shipped to.
HP-41 bar-code generation
rwiker's online bar-code generator
hookem88's HP41UC barcode generator download
Forth for the HP-41 (.pdf)
here and here are a couple of HP Museum forum topics on Forth for the 41
Forth-41 documents, including Ángel Martin's very clear MCode guide done in Apr 2014
MCODE wiki
Geir Isene's HP-41 pages
Matthias Werli's HP collection
Jeff's calc page
Jeff's Emu41 page
Jeff's HPIL resource page
HP-IL Compendium: The Hewlett-Packard Interface Loop peripherals repository, by Sylvain Côté
over 200 HP-41 programs in Jean-Marc Baillard's collection
MoHPC's HP-41 software library
Math in Silicon (.pdf)
module database on calc.fjk.ch
module database on Matthias Wehrli's hp-collection.org
Advantage ROM: Valentin Albillo's write-up (.pdf)
Valentín Albillo's website with lots of HP calculator articles, programs, photos, brochures, etc.
manual for Ángel Martin's 41z module which gives a true 4-level complex stack and tons of complex-number functions and enhancements written in MCode for maximum performance.  The manual is also available here, in case you don't want to sign up on hp41.org to download it.
manual for Ángel Martin's Sandmath module which gives gobs of math extensions for the HP-41.  The manual is also available here, in case you don't want to sign up on hp41.org to download it.
manual for Ángel Martin's Warp_Core module (.pdf) which is a further improvement on his 2015 Total_Rekall Module which offers RCL math on steroids, and full stack tests, to make programs in any discipline faster and more compact.  The Warp_Core module has plenty of additional features, like a menu-like function of XEQ+ which is useful when you can't remember the exact spelling of the function you want, LASTF (last function) now useful for the last five, a SELECT CASE structure, more-complex functions like M>= IND Z? and more.  A list of the new materials starts on page 7.
More modules from Ángel Martin
Håkan Thörngren's 'Ladybug' module giving the 41 a new customizable binary integer mode, with most HP-16C capabilities, and stack items up to 64-bit (the last 8 bits being kept in a buffer).  Does arithmetic, bitwise, and logical operations in bases 2, 8, 10, and 16.  (Everything is in the .zip file there.)
HEPAX quick-reference card (.pdf)
keyboard overlay generator
HP manuals, discussion by Richard Nelson on p.26 (.pdf)
HP calcs wiki
Floppy Days Vintage Computer Podcast with Randy Kindig, #59 (May 2016), "The HP41C Calculator, Part I, History with Richard Nelson and Gene Wright"
Floppy Days Vintage Computer Podcast with Randy Kindig, #60 (June 2016), "The HP41C Calculator, Part II, History with Richard Nelson and Gene Wright"  Randy asked me for a recording on how I got into the HP-41, and he put that at the beginning of the podcast.
How I got into HP-41
My HP-41 alarms and daytimer program
My HP-41 program to track time spent on various jobs

Email me at wilsonmines@dslextreme.com if you have suggestions for additional links, corrections, or to report dead links.  Please, no SEO spam!  You can use this email address for individual discussion too; but for forum-type discussion, use 6502.org's forum for 6502-related discussions (Note!  We absolutely do not tolerate spam!) and HP Museum's forum or hp41.org's forum for HP-41 discussions.  HP41.org's forum is 41-specific, but it does not have much traffic at all compared to HP Museum's which is for all the HP calculators, including ones being made today. 

last updated Sep 19, 2019