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

microprocessor A microprocessor is a computer processor (computing), processor for which the data processing logic and control is included on a single integrated circuit (IC), or a small number of ICs. The microprocessor contains the arithmetic, logic, a ...

from MOS Technology, Inc. It is a version of their 40-pin 6502 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 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

video game console A video game console is an electronic device that Input/output, outputs a video signal or image to display a video game that can typically be played with a game controller. These may be home video game console, home consoles, which are generally ...

and peripherals for the Atari 8-bit computers including the 850 Serial & Parallel Interface, and the 810 and 1050 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, cassette, 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, ...

slot, which only allows for 4KB of the external memory to be addressed. The other 4KB is reserved for the internal RAM 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 computer Home computers were a class of microcomputers that entered the market in 1977 and became common during the 1980s. They were marketed to consumers as affordable and accessible computers that, for the first time, were intended for the use of a s ...

s based on the 650x 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

semiconductor A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...

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 (A0..A12) and 8 data pins (D0..D7). The seven remaining pins are used for power (Vss, Vcc), the CPU timing clock (φ0, φ2), to reset the CPU (the /RES pin), 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 (the R/W pin). 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