The MOS Technology 65xx series is a family of

8-bit In computer architecture, 8-bit integers or other data units are those that are 8 bits wide (1 octet). Also, 8-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers or data buses of ...

microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circu ...

s from

MOS Technology MOS Technology, Inc. ("MOS" being short for Metal Oxide Semiconductor), later known as CSG (Commodore Semiconductor Group) and GMT Microelectronics, was a semiconductor design and fabrication company based in Audubon, Pennsylvania. It is mo ...

, based on the

Motorola 6800 The 6800 ("''sixty-eight hundred''") is an 8-bit microprocessor designed and first manufactured by Motorola in 1974. The MC6800 microprocessor was part of the M6800 Microcomputer System (latter dubbed ''68xx'') that also included serial and paral ...

(introduced ca. 1975). The 65xx family included the

6502 The MOS Technology 6502 (typically pronounced "sixty-five-oh-two" or "six-five-oh-two") William Mensch and the moderator both pronounce the 6502 microprocessor as ''"sixty-five-oh-two"''. is an 8-bit microprocessor that was designed by a small te ...

, used in home computers such as the

Commodore PET The Commodore PET is a line of personal computers produced starting in 1977 by Commodore International. A single all-in-one case combines a MOS Technology 6502 microprocessor, Commodore BASIC in read-only memory, keyboard, monochrome monitor, ...

and

VIC-20 The VIC-20 (known as the VC-20 in Germany and the VIC-1001 in Japan) is an 8-bit home computer that was sold by Commodore Business Machines. The VIC-20 was announced in 1980, roughly three years after Commodore's first personal computer, the ...

, the

Apple II The Apple II (stylized as ) is an 8-bit home computer and one of the world's first highly successful mass-produced microcomputer products. It was designed primarily by Steve Wozniak; Jerry Manock developed the design of Apple II's foam-mold ...

, the

Atari 800 The Atari 8-bit family is a series of 8-bit home computers introduced by Atari, Inc. in 1979 as the Atari 400 and Atari 800. The series was successively upgraded to Atari 1200XL , Atari 600XL, Atari 800XL, Atari 65XE, Atari 130XE, Atari 800XE ...

, and the British

BBC Micro The British Broadcasting Corporation Microcomputer System, or BBC Micro, is a series of microcomputers and associated peripherals designed and built by Acorn Computers in the 1980s for the BBC Computer Literacy Project. Designed with an empha ...

. The 6501 and 6502 have 40-pin DIP packages; the 6503, 6504, 6505, and 6507 are 28-pin DIP versions, for reduced chip and circuit board cost. In all of the 28-pin versions, the pin count is reduced by leaving off some of the high-order address pins and various combinations of function pins, making those functions unavailable. Typically, the 12 pins omitted are the three not connected (NC) pins, one of the two Vss pins, one of the clock pins, the SYNC pin, the set overflow (SO) pin, either the maskable interrupt or the non-maskable interrupt (NMI), and the four most-significant address lines (A12–A15) are the 12 pins omitted to reduce the pin count from 40 to 28. The omission of four address pins reduces the external addressability to 4 KB (from the 64 KB of the 6502), though the internal PC register and all effective address calculations remain

16-bit 16-bit microcomputers are microcomputers that use 16-bit microprocessors. A 16-bit register can store 216 different values. The range of integer values that can be stored in 16 bits depends on the integer representation used. With the two mos ...

. The 6507 omits both interrupt pins in order to include address line A12, providing 8 KB of external addressability but no interrupt capability. The 6507 was used in the popular

Atari 2600 The Atari 2600, initially branded as the Atari Video Computer System (Atari VCS) from its release until November 1982, is a home video game console developed and produced by Atari, Inc. Released in September 1977, it popularized microprocess ...

video game console, the design of which divides the 8 KB memory space in half, allocating the lower half to the console's internal RAM and peripherals, and the upper half to the Game Cartridge, so Atari 2600 cartridges have a 4 KB address limit (and the same capacity limit unless the cartridge contains

bank switching Bank switching is a technique used in computer design to increase the amount of usable memory beyond the amount directly addressable by the processor instructions. It can be used to configure a system differently at different times; for exampl ...

circuitry). One popular 6502-based computer, the Commodore 64, used a modified 6502 CPU, the 6510. Unlike the 6503–6505 and 6507, the 6510 is a 40-pin chip that adds internal hardware: an 8-bit parallel I/O port mapped to addresses 0000 and 0001. The 6508 is another chip that, like the 6510, adds internal hardware: 256 bytes of SRAM and the same 8-bit I/O port featured by the 6510. Though these chips do not have reduced pin counts compared to the 6502, they need 8 new pins for the added parallel I/O port. In this case, no address lines are among the 8 removed pins.

References

External links

MOS 6508 datasheet (GIF format, zipped)
{{MOS CPU 65xx microprocessors