Commodore PET

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#02 MOS Technology 6502 Processor: Architecture, History, and Computers

1. Architecture and Design The MOS Technology 6502 is an 8-bit microprocessor with a 16-bit address bus, built using 8μm NMOS technology with 4528 transistors (3510 enhancement and 1018 depletion load). The die size is 3.9 × 4.3 mm (16.6 mm²), and it requires a single +5V power supply. Pinout diagram of the MOS 6502 microprocessor showing all 40 pins, including address and data buses and control signals 1.1 Internal Organization The 6502 has a minimalist register set consisting of only 6 registers: 8-bit registers: 16-bit register: Unlike the Z80, the 6502 has no register pairs – all 16-bit operations must be performed through separate instructions for the low and high byte. Little-endian Architecture The 6502 is a little-endian processor, meaning 16-bit values are stored with the low byte first. For example, address $1234 is stored in memory as $34 $12. Zero Page One of the 6502’s key features is the Zero Page – the first 256 bytes of memory ($0000–$00FF) act like pseudo-registers. Instructions referencing the Zero Page: The stack is permanently located on page $01 ($0100–$01FF). 1.2 Addressing Modes The 6502 offers 13 addressing modes, including: Mode Example Operation Immediate LDA #$EA A ← $EA Absolute LDA $0314 A ← M($0314) Absolute,X LDA $0314,X A ← M($0314+X) Zero Page LDA $02 A ← M($02) Zero Page,X LDA $02,X A ← M($02+X) (Zero Page,X) LDA ($02,X) A ← M(PTR($02+X)) (Zero Page),Y LDA ($02),Y A ← M(PTR($02)+Y) 1.3 Instruction Set The 6502 has 56 basic instructions (compared to the Z80’s 158). With different addressing modes, this totals 151 opcodes. Categories include: 2. History of Creation 2.1 Founding of MOS Technology The 6502 story began in 1973, when Chuck Peddle was working at Motorola on the 6800 processor. Peddle saw market demand for a much cheaper processor than the ~$300 solutions of the time. When Motorola’s management rejected his proposal, he left the company. In August 1974, he and seven other Motorola engineers – Harry Bawcom, Wil Mathys, Rod Orgill, Ray Hirt, Mike Janes, Terry Holdt, and Bill Mensch – joined MOS Technology in Valley Forge, Pennsylvania. Chuck Peddle and his team displaying a large layout of the MOS 6502 microprocessor / team6502.org 2.2 Design Team MOS Technology was a small semiconductor firm founded by John Paivinen, a former GE colleague of Peddle. The company specialized in calculator chips and had its own mask lab and production line. The “Motorola Eight” team included: 2.3 Design Process The 6502 was largely designed by hand on paper. Without advanced simulation tools, most verification was done mentally or with basic aids. Key innovations included: 3. Evolution and Variants 3.1 Basic Versions: 3.2 Later Extensions: 4. Computers Using the 6502 4.1 American Pioneers: Apple II, By All About Apple museum official web site – http://www.allaboutapple.com/, CC BY-SA 3.0 Atari 800, By Evan-Amos – Own work, Public Domain 4.2 Game Consoles: Atari 2600, By Evan-Amos – Own work, Public Domain Nintendo Famicon, By Evan-Amos – Own work, Public Domain 4.3 British Systems: BBC Micro, By BBC_Micro.jpeg: Stuart Bradyderivative work: Ubcule (talk), Public Domain 4.4 Other European Implementations: 5. DIY Computers and Hobbyist Projects 5.1 Ben Eater 6502 Computer: 5.3 Other DIY Projects: 6. Modern Applications 6.1 Embedded Systems: The 65C02 is still produced by Western Design Center and used in: Bill Mensch claims 6502 derivatives are found in over 5 billion devices worldwide. 6.2 Educational Significance: The 6502 remains a perfect learning tool for: Its simplicity makes it ideal for newcomers to low-level computing.

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#02 The Holy Trinity of 1977 – How the Apple II, Commodore PET, and TRS-80 Defined the Home Computer

The year 1977 is widely regarded by IT historians as the birth of the home computer era. Within just a few months, the world saw the release of three groundbreaking machines that would forever change the computer market: the Apple II, Commodore PET, and TRS-80. These were the computers that helped transition personal computing from a hobbyist pursuit into a tool for daily use, a symbol of modernity, and the beginning of the digital revolution. Apple II – The First Truly Personal Computer for Everyone Release: June 1977 The Apple II was engineered by Steve Wozniak, whose technical brilliance, combined with Steve Jobs’s marketing vision, quickly conquered the market. Unlike many competitors, the Apple II was nearly ready to use straight out of the box: it had a built-in keyboard, composite video output that could connect to a standard TV, color graphics, and expansion card slots. A typical configuration with 4 KB of RAM cost $1,298, and the computer was immediately well-received by programmers, schools, and small businesses. The true “killer app” for the Apple II was VisiCalc — the first spreadsheet program — which transformed the computer into a practical business tool. The Apple II became the educational standard in American schools, and total sales eventually exceeded six million units. Fun fact:Steve Wozniak insisted that the Apple II be as quiet as possible, which is why the machine was designed without a fan. Users joked that the computer was “as quiet as a mouse” — a trait that became part of its appeal. Apple II with monitor – Author: Bilby, Wikimedia Commons, CC BY-SA 3.0 Commodore PET 2001 – A 1970s “All-in-One” Machine Release: January 1977 (first deliveries: October 1977) The Commodore PET (Personal Electronic Transactor) was the brainchild of Jack Tramiel, a Polish immigrant and head of Commodore. The PET was the first computer presented at CES 1977 and arguably the most school-oriented of the three: it featured an all-in-one chassis with a built-in rubber keyboard, monochrome monitor, and cassette drive for saving programs and data. It was also the first mass-produced computer to come standard with the BASIC language, licensed from Micro-Soft. Although the initial version, with 4 KB RAM, cost $795, the PET quickly became popular in schools, laboratories, and even some offices. Its aesthetic design reflected the 1970s science fiction style, and its durability and simple construction laid the foundation for Commodore’s future success. Anecdote:The earliest PETs came with a “chiclet” keyboard — soft, rubbery keys that were extremely fragile. Students could break them on first use! Commodore quickly replaced them with traditional keyboards in the PET 2001-N model. Commodore PET 2001 – Author: Rama, Wikimedia Commons, CC BY-SA 2.0 FR Tandy TRS-80 – The Mass – Market Computer from Radio Shack Release: August 1977 The TRS-80 Model I was Radio Shack’s answer to the growing home computer market. Like the Apple II, it could be connected to a TV or dedicated monitor, and it came equipped with a keyboard and cassette recorder. Its key advantage was availability — it could be purchased immediately at nearly any Radio Shack location. The price for the full package (including monitor and cassette recorder) was just $599, making the TRS-80 the most affordable of the “Holy Trinity.” Initially, the TRS-80 was mocked by users, earning the nickname “Trash-80” due to keyboard issues and faulty cassette drives. But within six months, sales exceeded 10,000 units per month, and by 1981, nearly a quarter million units had been produced. Thanks to its wide availability, user community, and affordable support (including service and training at Radio Shack stores), the TRS-80 gained popularity in education and small businesses. Fun fact:There’s a well-known story from early 1978 in which the TRS-80 temporarily displaced calculators on store shelves — customers convinced salespeople that the computer could replace calculators entirely! TRS-80 Model I – Author: Bilby, Wikimedia Commons, CC BY-SA 3.0 The Holy Trinity – The Beginning of the Real Personal Computer Market The release of the Apple II, Commodore PET, and TRS-80 set the standard for the home microcomputer market. Each of these machines was affordable, relatively easy to use, and backed by companies determined to “put a computer in every home.” By 1979, these three computers together made up over half of the U.S. computer market. From that point on, computers were no longer the domain of laboratories and hobbyist clubs — they made their way onto the desks of students, teachers, and small business owners. These were the machines that brought computing into daily life, marking the beginning of a new era: the era of personal computers. In the next episode: We’ll explore the global 8-bit explosion — the rise of the ZX Spectrum, Commodore 64, Atari 400/800, and the first golden age of home coding and gaming!

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