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MOS Technology VIC
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{{distinguish|text=its more advanced successor used in the C64 and C128, the [[MOS Technology VIC-II|VIC-II]]}} [[Image:MOS 6561 VIC.jpg|thumb|MOS Technology VIC (PAL version 6561β101)]] [[Image:MOS 6560 pinout.svg|thumb|right|220px|Pinout diagram of the 6560 version of the MOS VIC chip. This circuit was packaged in a standard 40-pin [[Dual in-line package|DIP]] casing.]] <!-- Deleted image removed: [[Image:Yes VIC can.png|thumb|right|220px|MFLI [[Commodore VIC-20 demos|demo]]]] --> The '''VIC (Video Interface Chip)''', specifically known as the '''[[MOS Technology]] 6560''' ([[NTSC]] version) / '''6561''' ([[PAL]] version), is the [[integrated circuit]] chip responsible for generating video graphics and sound in the [[VIC-20]] [[home computer]] from Commodore. It was originally designed for applications such as low-cost [[cathode-ray tube|CRT]] [[computer terminal|terminals]], biomedical monitors, control system displays and [[arcade game|arcade]] or home [[video game console]]s. The chip was designed by Al Charpentier in 1977 but Commodore could not find a market for the chip. In 1979, [[MOS Technology]] began work on a [[Video Display Controller|video chip]] named ''MOS Technology 6564'' intended for the ''TOI'' computer and had also made some work on another chip, ''MOS 6562'' intended for a color version of the [[Commodore PET]]. Both of these chips failed due to memory timing constraints (both required very fast and thus expensive [[Static random-access memory|SRAM]], making them unsuitable for mass production). Before finally starting to use the VIC in the VIC-20, chip designer [[Robert Yannes]] fed features from the 6562 (a better sound generator) and 6564 (more colors) back to the 6560, so before beginning mass production for the VIC-20 it had been thoroughly revised. Its features include: * 16 kB address space for screen, character and color memory (only 5 kB points to [[Random-access memory|RAM]] on the VIC-20 without a hardware modification) * 16 colors (the upper 8 can only be used in the global background and auxiliary colors) * two selectable character sizes (8Γ8 or 8Γ16 bits; the pixel width is 1 bit for "hires" characters and 2 bits for "multicolor" characters) * maximum video resolution depends on the television system (176 Γ 184 is the standard for the VIC-20 firmware, although up to 248 Γ 232p/464i is possible on the [[NTSC]] machine and up to 256 Γ 280 is possible on the [[PAL]] machine<ref>From ftp://www.zimmers.net/pub/cbm/documents/chipdata/VIC-I.txt</ref>) * 4 channel [[Programmable Sound Generator|sound system]] (3 square wave + "white" noise + global volume setting) * on-chip [[Direct memory access|DMA]] * two 8-bit [[analog-to-digital converter]] * [[light pen]] support Unlike many other video circuits of the era, it does not offer [[Dynamic random-access memory|dynamic RAM]] [[Memory refresh|refresh]] capabilities. Thus the VIC-20 employed the more expensive static RAM (SRAM) chips. This is likely the reason why the machine was sold with just 5 KB of RAM. Memory expansions for the VIC-20 either used SRAM as well or implemented their own refresh circuit. The VIC was programmed by manipulating its 16 [[control register]]s, memory mapped to the [[memory address]] range $9000–$900F in the VIC-20 address space. The on-chip A/D converters were used for dual [[paddle (game controller)|paddle]] position readings by the VIC-20, which also used the VIC's [[light pen]] facility. The VIC preceded the much more advanced [[MOS Technology VIC-II|VIC-II]], used by the VIC-20's successors, the [[Commodore 64|C64]] and [[Commodore 128|C128]]. VIC-20s with expansion RAM have their video memory (550 bytes) at $1000 and when it is not present, $1E00. User-defined [[character set]]s must be placed within the first 5k of system RAM. The default [[PETSCII]] character ROM is at $8000 and each character takes 8 bytes to store. Up to 128 characters may be used at any one time. While the PET had a backslash (\) in its character set, this was replaced on the VIC-20 (and all subsequent Commodore machines) with a British pound sign (Β£). Programmable characters are the only way of creating graphics and animation on the VIC as the chip does not have sprites or an all-points-addressable bitmap mode. Of the 16 colors in the palette, eight may be used for the foreground (per the color RAM at $9400) and border while the others are limited to the background and auxiliary multicolors. The MSB of the color RAM is a flag used to indicate if that character is multicolor or high resolution. Due to the extreme blockiness of the former, most VIC-20 games use hires characters. The VIC does not support scrolling or raster interrupts like on the VIC-II, but the scanline counters could be polled for a specific point on the screen to produce raster effects. This feature was rarely used in games except for a few titles like Imagic's [[Demon Attack]]. Sound programming on the VIC is done by placing a frequency value in one of the four registers at $900A-$900D (they are turned off by writing a zero to them). The first three are square wave generators pitched half an octave from each other and the fourth is for white noise.
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