Some thoughts on the 6502 Technology

August 21, 2010 Leave a comment

For text in full-length, see

6502, why it is so important?

The first 6502 microprocessor was designed by Chuck Peddle and Bill Mensch in 1975 for MOS Technology, also known as CSG (Commodore Semiconductor Group), was a semiconductor design and fabrication company based in United States. 6502 is a low cost full-featured microprocessor. 6502 was originally second-sourced by Rockwell and Synertek and later licensed to a number of companies. It’s one-sixth the price ($25) of the similar products from other well established competitors ($179, Intel 6800).  Since the cost in building a computer has been lowed at that time, it eventually result in home computer revolution of the 1980s. Nowadays, 6502 is still made for embedded systems and video game console.

6502 bought the Home Computer Revolution

Due to their cost are low,  the 6502 and Z80 bought us to the age of “Home Computer Revolution” in 1980s. 6502 home computers such as: Commodore RadioShack TRS-80, Commodore PET, Apple II, BBC Micro, Atari 800XL, etc were appeared in consumer market in 1980s.  People started to have their own computers.  (My father bought an Apple ][ computer in 1983 with HK$4500 (which is around US $600).)

At that time, most of the 6502  home computers come with a BASIC interrupter.  And the software are mainly written in BASIC or assembly languages.

History of 6502 Technology

A  6502 processor is firstly packaged in a DIP-40 plastic package and was designed by the same development team that had designed the Motorola 6800. Thus, 6502 and 6800 process a lot of similarities, such as: single accumulator and small number of registers. In addition, the 6502 processor introduces the idea of “zero page” which improves the speed of communication. A 6502 can also be used to handle BCD calculation.

The first development board of 6502 processor launched to the market was MDT-650. Then KIM-1, Rockwell AIM65 and Synertek SYM-1 were also launched to the market. Those 6502 development boards were welcomed to both engineers and hobbyists, thus it leaded to widespread acceptance to the market.

One of the first publicly marketed computers using the 6502 technology was the Apple I computer in 1976. Later, there are Apple II and Commodore PET, Atari home computers, BBC Micro family, etc came to the market and bought the trend of 6502 computers.

6502 processor not only bought great influences to computers market, it developed the video game console, too. Most of the video game consoles uses refined version of 6502 processors.  The first video game console which uses 6502 technology was the Atari 2600. Atari 2600 uses a simplified version of 6502, 6507 which can only address 8KB memory.


Update August 6, 2010, 6502 Assembly

August 6, 2010 Leave a comment

The instruction sets manual for the Arithmetic Operations have been updated.  The updated pages involved:

  1. Arithmetic Operations
  2. ADC – ADC, Add with Carry
  3. DEC – DEC, Decrement Memory
  4. DEX – DEX, Decrement X
  5. DEY – DEY, Decrement Y
  6. INC – INC, Increment Memory
  7. INX, INX – Increment register X
  8. INY – INY, Increment Y
  9. SBC – SBC, Subtract with Carry
  10. 6502 Instruction Set
  11. Op-codes Table
  12. Opcode of LDA Instructions

Happy Programming


Update July 26, 6502 Assembly

July 25, 2010 Leave a comment

The Logical Operations session of the 6502 Instruction set has been updated, the following pages have been involved:

Happy Programming ,


Update July 24, 6502 Assembly

July 24, 2010 Leave a comment

Four instructions under the categories of  Stacks Related Operations have been updated:

  1. PHA —    PHA stands for PusH Accumulator
  2. PHP —    PHP stands for PusH Processor status (SR)
  3. PLA —    PLA stands for PulL Accumulator
  4. PLP —    PLP stands for PulL Processor status (SR)

Happy Programming,


Update Content 23/7, 6502 Assembly

July 23, 2010 Leave a comment

This morning, before I left my home, I had updated Register Transfer Operations session of the 6502 instruction set manual.

There are totally six commands have been updated:

  1. TAX
  2. TAY
  3. TXA
  4. TYA
  5. TSX
  6. TXS

I have found out and removed some strange links generated from google site.  These were caused by links consisting different fonts setting.  That’s why some strange page have been found from google search on my website. Another problem is that, when I use IE 8 to edition the 6502 website, I found I cannot scroll down when I have click the view HTML button in the google site interface.  So, I had to edit the page using Firefox this morning.

Happy Programming,


Update Content on July 22, 6502 Assembly

July 22, 2010 Leave a comment

Today, I’ve spent some time to review the content of the 6502 Assembly Web-site. I found the description of all the 6502 instruction-sets are too concise and I need to rewrite them all.

However, it involves more than 60 pages, so I cannot rewrite them all at once. The first batch of the 6502 instruction sets involves Memory Operation and I completed rewriting this morning.

These include the following pages:

  1. LDA – LDA Instruction, Load Accumulator
  2. LDX – LDX Instruction, Load X
  3. LDY – LDY Instruction, Load Y
  4. STA – STA Instruction, Store Accumulator
  5. STX – STX Instruction, Store X
  6. STY – STY Instruction, Store Y

They are about 1/10 of the pages.  Stop by now,

Happy Programming,


Categories: 6502 Assembly Tags: , , , , , ,

Welcome to the world of 6502!

July 16, 2010 Leave a comment

I’ve been doing equipment design since 2006.  I started by using a Megawin 6502 MPU writing code for communication to a PC using USB. The experiment board also include several push buttons, Flash Memory and FRAM.  I found myself interested in programming 6502 Assembly language.

After some years,  I don’t want part of my works only stored in one of my portable hard disk.  I may lost all the data if the hard disk is corrupted.  So, I set up the 6502 Assembly website for organizing the material related to the topics.

Actually, my first 6502 program was written in 1988 (I was a small boy at that year) using an Apple II computer.  I am still remember the happiness, at that time, people treated you as a genius if you could write assembly programs.

By the way, that’s only part of my memory. I still enjoy writing 6502 assembly nowadays.  So, why not give a warm welcome to the world of 6502 Assembly.

Happy Programming,


Categories: 6502 Assembly