MOS Technologies

company A microprocessor design company started by some

ex-Motorola designers, shortly after the Intel 8080 and

Motorola 6800 appeared, in about 1975. MOS Technologies

introduced the 650x series, based on the Motorola 6800

design, though they were not exact clones for legal reasons.

The design goal was a low-cost (smaler chip) design, realized

by simplifying the decoder stage. There were no instructions

with the value xxxxxx11, reducing the 1-of-4 decoder to a

single NAND gate. Instructions with the value xxxxxx11

actually executed two instructions in paralell, some of them

useful.

The 6501 was pin-compatible with the 6800 for easier market

penetration. The 650x-series had an on-chip clock oscillator

while the 651x-series had none.

The 6510 was used in the Commodore 64, released September

1981 and MOS made almost all the ICs for Commodore's pocketcalculators.

The PET was an idea of the of the 6500 developers. It was

completly developed by MOS, but was manufactured and marketed

by Commodore. By the time the it was ready for production

(and Commodore had cancelled all orders) MOS had been taken

over by Rockwell (Commodore's parent company). Just at this

time the 6522 (VIA) was finished, but the data sheet for it

was not and its developers had left MOS. For years, Rockwell

didn't know in detail how the VIA worked.

(2001-03-31)