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First of all, the 6522 has some things (parallel ports and timers) that a UART simply doesn't have at all. A UART will normally generate some programmable number of start bits, stop bits, and possibly parity bits. The number of data bits will typically also be programmable (e.g., on an 8250, anywhere from 5 to 8 data bits). Insertion of the start and stop ...


11

[Not sure if I understand the question in full] A parallel port chip like the 6522 is about providing port lines. In case of a 6522 these are 16 lines (two 8 bit ports) for arbitrary use plus 4 control lines with restricted use. Like with any other interface, a designer adds as many as he needs. In case of the VIC-20 the schematics show that of the first ...


8

Commodore owned MOS technologies, who made the VIA chips. Although the VIC-20 might have been able to replace a VIA chip with a 4051, a 74LS139, a couple of 74LS373s, and eight resistors, I don't know that doing so would have really saved anything compared to the in-house cost of the VIA. Further, using a second VIA made it possible for them to have one ...


6

TL;DR: UART is a generic term for a serial interface function (chip) for asynchronous transmission. In contrast 6522 is a specific chip - which does not include UART functionality. Implementation for UARTs were done by next to every manufacturer, each using names (and numbers) of their own, like Intel's UART 8250 / 8251, Zilog's Z80-SIO (Z8440) or Serial ...


2

Referring specifically to the serial communication functionality of the VIA, there is a very crucial difference between that and a UART. (It is not unusual for a UART to also include some GPIO pins and a timer or two, as for example the 28L92 does.) UART stands for Universal Asynchronous Receiver & Transmitter. Asynchronous here means that no explicit ...


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