Original Amiga chipset

OCS means Original (or Old) Amiga Chipset . It was followed Extended chipset (ECS).

It was provided with the A1000, like the A500 and the A2000. New A500 and A2000 were produced with the ECS, or a mixture of OCS and ECS.

The tiddlywinks which gave to Amiga its single graphs consisted of three called integrated circuits, Agnus, Denise, and Paula. Two chips the CIA are not regarded as belonging to the OCS or the ECS, having been used before in the Commodore 64 and Commodore 128.

Denise

Denise was a chip nonprogrammable person in charge of the transfer of the raw data of the IC hybrid to port RVB.

Agnus

Agnus provided in fact the possibilities multi-media:

Providing DMA for the sound and the graphs
Handling the memory (512 Kio of Chip RAM, memory which can be reached by the processor and the chipsets)
video Synchronization (versions STAKE or NTSC)
Containing the logic of the coprocessors Copper and Blitter.

A new version of Agnus was employed in the major part of the versions of A500, and A2000, called Fat Agnus, which could handle 1 Me Chip RAM on the mother chart. Super Agnus, a version even more recent was able to support 2 Me Chip RAM, and could also change between a video signal STAKE and NTSC.

Resolutions

The lowest resolution of Amiga (sometimes called LoRes for the low resolution) is 320×200 (60 Hz, NTSC), or 320×256 (50 Hz, STAKE). In these resolutions, it could post 2,4,8,16 or 32 colors simultaneously on a pallet of 4096 colors (4 bits for each component RVB). The resolution can also be increased horizontally (HiRes or modes of high-resolution), from 320 to 640, but by limiting the maximum number of colors usable to 16.

The vertical resolution was 200/256 and could be doubled to 400/512 with the use of the video entrelaçage.

Amiga can also increase its posting of some pixels moreover in each direction, by effectively employing space apart from the 320×200, making all posting accessible to the programs. This device is called Overscan.

Colors

The number of colors on the screen could be also increased by two methods:

the Mode Halfbrite or EHB for Extra Half Bright - an additional plan is used to post 64 colors, but the 32 second colors were half less brilliant than the 32 first, useful only by using the pallet attentively. This device was absent from first versions of the chipset.
the Mode HAM , or Hold-And-Modify - here still six plan are used, but only 16 colors are defined in the pallet, the 48 “colors” remaining; describe how to modify the preceding color of the pixels. It was possible to post the whole pallet of 4096 colors, even with the registers of the initial pallet in black. But, a badly adapted configuration of the palette can produce much frangeage. Thanks to a more rigorous selection of the colors, it was possible to post images like photographs and probably to use all the 4096 colors with a minimum of frangeage, that many spectators do not even notice.

Video synchronization

Video synchronization was deliberately selected to make it possible to use Amiga with televisions, but this also exigait an additional component called “modulator TV” which left only one monochromic image. There was a connector RVB separated to connect a monitor, through a connector to measure of 23 pins of the type D-sub, enriches by entries and digital displays/analogical.

In normal circumstances, Amiga produces its own signals of video synchronization, but the chipset can also use an external synchro via the connection RVB of the monitor to authorize the genlocking with an external video. There is also a bit on this connector which indicates if Amiga produced an image (in opposition to the prime coat), allowing a covering (Overlay) easy of the video of Amiga on the external video.

This made Amiga particularly gravitational like system of titration of vidéos and emissions, because it avoided expenditure in material of Chromakey and “AB roll” which would have been made necessary without the use of genlock.

The support of the overscan, interlacing, the possibilities of genlocking, and the fact that the synchronization of posting was very close to the emission standards (NTSC or STAKE), made of Amiga the ideal computer for the video, and indeed, it was used in many studios to digitize of the video sequences, to subtitle and interact between the vidéos.

Other characteristics

the framebuffers function in planar mode.
the graphic capacities are very difficult to briefly explain because of the coprocessor Copper, which makes it possible in the course of sweeping to change the characteristics of posting (resolution, palette, many colors, synchronization of sweeping, réaffectaction and/or modification of the sprites, etc).
thanks to the Copper, one can have a screen separated into two in the horizontal plane, with different resolutions and pallets on each part of the screen.
8 sprites material (used for the pointer of mouse for example) of a width of 16 pixels and a variable height with 3 colors (more one fourth “color” for the mask of transparency). Two sprites can be joined to make a single sprite of 15 colors.

although it is not an official characteristic, the Copper can be used to change the registers of sprite (inter alia) in the middle of a line of sweeping. What makes it possible to post more sprites by line. An easy way which was employed by certain plays like Battle Squadron .
it is possible to simulate a variable width of sprite while placing sprites of 16 pixels of broad side by side. And this until the maximum of 128 pixels broad for sprites of 3 colors, and 64 pixels broad for sprites of 15 colors. However, broader is this pseudo-sprite, less it is possible to post sprites on a line of sweeping.

Paula

possibilities of sound of Paula:

made stereo by material DMA of 4 channels. Samples of 8 bits PCM until the sampling rate of 28867 Hz.
separate pointer sampling rates for each of 4 channels DMA.
Possible to emulate sound 14 bits with the DMA, by modulating 2 channels and the adjustment of volume on 6 bits.
dynamic sound 8 bits == 48.165 DB.
Each channel has a register of volume on 6 bits.

Others

Blitter

Blitter is a very powerful coprocessor in handling of large storage blocks. It is more particularly dedicated on Amiga to the graphic handling operated on great rectangular zones (fillings, obliterations, duplications, etc) and to the creation of special effects (e.g. plasma effect). Owing to the fact that it is given rhythm to 71 MHz, is 10 times the speed of a Motorola 68000, it is able to carry out the following operations much more quickly:

copy (transfer) of block (p. e.g. animation, scrolling vertical)
shift of block (p. e.g. scrolling horizontal)
logical operations (p. graphic e.g. filters)
masking (p. e.g. copies, treatment of the collisions)
traced straight lines (p. e.g. vectorial drawing 2D, 3D)
filling of block (p. e.g. vectorial drawing 2D, 3D)

Other specificities:

multiple registers of pointers and modulos (e.g zoom)
addressing ascending report or descendant (e.g scrolling)
detection of the zero (e.g collision detection)
addressing report linear or rectangular
4 channels DMA

an image on Amiga is made up of plans (bitmaps) superimposed. The combination of all the plans forms the image, the depth (the number of plans) making it possible to code the color of the pixel in the pallet selected. Blitter which can extremely quickly handle all the plans constitutive of the same image, even of several images, that enables him to carry out all operations necessary to displacement, filtering, management of the collisions or zoom of zones images on the screen.

the use of the blitter allows to the programmers plays to exceed the capacities of the processor of sprites and thus authorizes fluid animation characters or vehicles of giant size.

the logical possibilities of operations on the blocks allows in real-times of many effects of video filtering.

the use of channels DMA makes it possible Blitter independently to reach the memory of the principal processor, from where the extreme fluidity of the multidirectional scrollings and the vidéos treatments on Amiga. The blitter makes it possible the processor not to be solicited by this kind of needy work and remains thus available for other tasks.

Copper

Copper, Co-processeur of 3 instructions functioning the processor parallel to, which makes possible the creation of effects special graphic with a load processor and minimal intervention. It carries out a list of instructions called Copperlist. The copper is synchronized with the sweeping of the screen and thus makes it possible to program events according to position of the electron beam.

It was very useful to allow the vertical scrolling screens in the Workbench or to allow the posting of more than colors or sprites in the plays and the demonstrations.

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