MOS Technologies

MOS Technologies

(company)A microprocessor design company started by someex-Motorola designers, shortly after the Intel 8080 andMotorola 6800 appeared, in about 1975. MOS Technologiesintroduced the 650x series, based on the Motorola 6800design, though they were not exact clones for legal reasons.

The design goal was a low-cost (smaler chip) design, realizedby simplifying the decoder stage. There were no instructionswith the value xxxxxx11, reducing the 1-of-4 decoder to asingle NAND gate. Instructions with the value xxxxxx11actually executed two instructions in paralell, some of themuseful.

The 6501 was pin-compatible with the 6800 for easier marketpenetration. The 650x-series had an on-chip clock oscillatorwhile the 651x-series had none.

The 6510 was used in the Commodore 64, released September1981 and MOS made almost all the ICs for Commodore's pocket calculators.

The PET was an idea of the of the 6500 developers. It wascompletly developed by MOS, but was manufactured and marketedby Commodore. By the time the it was ready for production(and Commodore had cancelled all orders) MOS had been takenover by Rockwell (Commodore's parent company). Just at thistime the 6522 (VIA) was finished, but the data sheet for itwas not and its developers had left MOS. For years, Rockwelldidn't know in detail how the VIA worked.