The 6507 (typically "''sixty-five-oh-seven''" or "''six-five-oh-seven''") is an 8-bit

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 circ ...

from MOS Technology, Inc. It is a version of their 40-pin

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 ...

packaged in a 28-pin DIP, making it cheaper to package and integrate in systems. The reduction in pin count is achieved by reducing the

address bus In computer architecture, a bus (shortened form of the Latin '' omnibus'', and historically also called data highway or databus) is a communication system that transfers data between components inside a computer, or between computers. This e ...

from 16 bits to 13 (limiting the available memory range from 64 KB to 8KB) and removing a number of other pins used only for certain applications. To do this, A15 to A13 and some other signals such as the interrupt lines are not accessible. As a result, it can only address 8KB of memory, which for some applications at the time (1975) was acceptable and not overly restrictive. The entire 6500 CPU family was originally conceived as a line of very low-cost microprocessors for small-scale embedded systems. The 6507 and 6502 chips use the same underlying silicon layers, and differ only in the final metallisation layer. This ties the interrupt lines to their inactive level so they are not vulnerable to generating spurious interrupts from noise. The first three digits of the chip identifier are part of the silicon layers, and the final digit is in the metallisation layer. Micro-photography of the 6502 and 6507 shows this difference. Atari-2600-Console

The 6507 is widely used in two applications: the best-selling

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 microprocesso ...

video game console A video game console is an electronic device that outputs a video signal or image to display a video game that can be played with a game controller. These may be home consoles, which are generally placed in a permanent location connected to ...

and

Atari 8-bit family 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, ...

peripherals including the 850 Serial & Parallel Interface, and the 810 and

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disk drives. In the 2600, the system is further limited by the design of the

ROM cartridge A ROM cartridge, usually referred to in context simply as a cartridge, cart, or card, is a replaceable part designed to be connected to a consumer electronics device such as a home computer, video game console or, to a lesser extent, elect ...

slot, which allows for 4KB of external memory to be addressed. The other 4KB is reserved for the internal

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and I/O chips, using a minimal-cost partial decoding technique that causes the RAM and peripheral device registers to appear at multiple aliased addresses throughout the 4K address space. Most other machines, notably home computers based on the 6500 architecture, use either the standard 6502 or extended versions of it, in order to allow for more memory. By the time the 6502 line was becoming widely used around 1980, ROM and RAM

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memory prices had fallen to the point where the 6507 was no longer a worthwhile simplification. Its use in new designs ceased at that point, though the Atari 2600 that contains it continued to be sold into the early 1990s, as it was not discontinued until January 1, 1992. However, late-model Atari 2600 consoles do not necessarily contain a discrete 6507 chip.

Pin configuration

The 6507 uses a 28-pin configuration, with 13 address pins and 8 data pins. The seven remaining pins are used for power, the CPU timing clock, to reset the CPU, to request a CPU wait state during its next memory read access (the RDY pin), and for the CPU to indicate if a read or write memory (or MMIO device) access is being performed. There is no IRQ or NMI pin on the processor. The RDY pin is not included on all other 28-pin cut-down versions of the 6502. Within the Atari 2600, RDY is used to synchronise the CPU to the television video lines. This function is essential for the 'racing the beam' method used by the 6502 and Atari Television Interface Adaptor chip to generate the television video signal. In response to a specific address access, the TIA will assert RDY to halt the CPU until the end of the current video scan line.

Pin configuration

References

Further reading