12

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 ...


8

Preface: Speculations of an alternate history are unfit for RC.SE, so this answer is restricted to fact checking. TL;DR; From a software (Kernal) PoV there is no reason for using a 6526, but there are two indicators from the hurried design case and business case: Volume. The new 652x family member (*1) was designated to be the base I/O chip for all upcoming ...


8

Klaus Dorman's functional tests for the 6502 are fantastic: https://github.com/Klaus2m5/6502_65C02_functional_tests


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 ...


3

I am unaware of any formalised test suite for either the 6520 or 6522. The 6526 is at least partially covered by Wolfgang Lorenz's C64 test suite. Because of the applicability to other machines, you usually see it documented for its 6502 tests (and the outward link to the suite itself there is broken; instead try that listed here) but it includes a ...


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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