The history of … Decimal mode (D) - set if the processor is in decimal mode. All external transfers are still 8 bit wide and address expansion is rather clumsy. Zero (Z) - set if the result is zero. The 6502 processor provides several ways in which memory locations can be addressed. IRQ disable (I) - set if the IRQ interrupt is disabled. The 6502 is a classic piece of computing history. Versions of this CPU were found in everything from the Apple ][, to the Nintendo Entertainment System, and the Commodore 64. The 6502 was a royal pain in the fundament when it came to code generation (my housemate wrote Deep Blue C for the Atari 800, and he admits it kind of sucked). There isn't a real schematic of the interior of the 6502 available (AFAIK), so I had to make my own based on 1) the "internal architecture of the 6502" published in many datasheets and 2) on how the 6502 behaves when executing commands. As a result the 65816's performance isn't much higher than a plain 6502. All 6502-based machines used 8-bit processor architecture, and in 1981, Intel was working towards a fully compatible 16-bit architecture to replace the 8086 used in the IBM PC/XT. For one, the 65816 is only a 16 bit CPU in a very restricted way. After studying up on the architecture of all these different CPUs, I decided that the 6502 was still the best choice to use as a model, because I believe it can be implemented using the least CPLD resources. The Apple II is powered by a very simple MOS 6502 CPU. Some instructions support several different modes while others may only support one. First I divided the 6502 into functional blocks: - CPU in/output - Instruction decoder - Program Counter I looked at the Intel 8008 and 8080, Zilog Z80, and Motorola 6800 and 6809, which were all popular 8-bit CPUs back in the 1970’s and 80’s. If the 6502/6809 architecture isn’t your cup of tea (or, you like to build many different types), there is the Build Your Own Z80 Computer. Atari 2600 uses a simplified version of 6502, 6507 which can only address 8KB memory. The main improvement wider architectures offer is plain management of large address space. The first video game console which uses 6502 technology was the Atari 2600. Carry (C) - set if there was a carry from or borrow to during last result calculation. We continually strive to remain the largest and most complete source for 6502-related information in the world. In native mode, the key point to remember is that 16-bit quantities are transferred between the CPU and memory one 8-bit byte at a time. In addition the two index registers can not always be used interchangeably. (The 6502 decimal mode and indirect jump bugs are fixed without requiring the extra cycle that the 65C02 requires.) But although I had my time programming in ASM (mainly for Motorola’s 68000 and 56000), I wanted a way to avoid plunging too deeply into the arcane of the 6502 architecture. is a resource for people interested in building hardware or writing software for the 6502 microprocessor and its relatives. 6502/650x instruction … Most of the video game consoles uses refined version of 6502 processors. The 6502 processor not only brought great influences to computers market, it developed the video game console, too. Instruction Set.