MOS Technology 6522
The versatile interface adapter 6522 (VIA ) is a flexible Ein-/Ausgabebaustein Company MOS Technology. He has two very powerful 16- bit interval timer, a seriell-nach-parallel/parallel-nach-seriell-Schieberegister and two individually programmable I / O ports of 8 bits each. To control these functions, there is an interrupt flag register, an interrupt enable register and a pair of function control register.
The 6522 was also manufactured by Rockwell Semiconductor and GTE under license.
The shift register error
The shift register has contained a design flaw, which is why it was not, as originally planned, to implement the CBM - bus ( " serial IEC bus ") in the Commodore VIC-20 used. Instead, this functionality is implemented completely in software. The result was that this bus could work with only about 1 /6 of the speed, as if the hardware support could have used.
In the CIAs 6526 of the successor model C64 said problem was fixed, but in the floppy VC1540 (and later the VC1541 ), the 6522 chips were still used. In addition, the then Commodore CEO Jack Tramiel decided to classify the backward compatibility with the VC20 important than the floppy speed, and so the same technique has been retained with their low speed. C128 only when in conjunction with the floppy VC1571 originally proposed technique has been realized, the so-called burst - mode.
- I / O- chip
- MOS Technology