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» Economics » Amiga » Topics begins with Z » Zorro bus

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The Zorro bus is a bus system and/or an internal interface of the Amiga computer.

It was used first as Zorro i in the Amiga 1000, further 16-bittig as Zorro II in the Amiga 2000 and finally 32-bittig (multiplexed) as Zorro III in the Amiga 3000 and more highly.

The bus system of the early Amiga models is the Zorro bus in such a way specified with 24-Bit-Adressraum - in the A500/1000 laterally by a 86poligen connection, in the A2000 Zorro II by several 100-polige of card locations, in the A3000/A4000 Zorro III with 32-Bit-Adressraum by several 100-polige of card locations, 32 bits was reached internally by multiplex ones of the signal lines. By an adapter one could operate Zorro II maps at an Amiga 500/1000. Of course also all Zorro II maps ran still at the Zorro III bus, since by the bus it was independently recognized whether it itself with the map around 16 - or 32-Bit-Karte acted.

Into the models A2000, A3000 and A4000 could be built also commercial IBM-compatible ISA plug-in cards (16-Bit), however for it additionally a so-called bridge map was necessary, and only non removable disks were accessible by special software also from the Amiga side.

Car Config mechanism

In addition the Zorro bus has a so-called car Config mechanism, which makes an automatic merging possible of extension cards with the system start. Each Zorro map has for it an EPROM or a PAL component, in which all necessary information for the car Config mode is contained. These are for example

  • Manufacturer index: Each developer of Zorro maps kept an index, over which he can assigned recognize its map with the expansion LIBRARY from Commodore and/or Amiga Technologies.
  • Product number: This number can be selected by the manufacturer freely and is additionally necessary for the recognition over the expansion LIBRARY.
  • Serial number: It can all possible freely by the manufacturer be selected and can mean (4 bytes).
  • Type name and flag: Here information stands, like the Zorro standard (II/CIII), the size of the necessary address area and some still more.

The address area can amount to 64 KByte, 128 KByte, 256 KByte, 512 KByte, 1 MByte, 2 MByte, 4 MByte and 8 MByte. Thus the system for the map reserves only so much memory, as is necessary.

With the Amiga 2000 configuring internal interfaces introduced for the first time. These internal interfaces of the Amiga are comparable with the today's PCI Slots of modern computers.

Each Zorro map has its own number, which depends on the card location, in which it is. After a RESET all maps are queried over the so-called signals CFGIN and CFGOUT. Each map gets 64 kilobyte a large information block assigned, which lies for Zorro II starting from $00E8xxxx and for Zorro III starting from $FF00xxxx. Then all necessary data for the integration of the map are registered into a system list. Afterwards the drivers are installed, which over the expansion LIBRARY all necessary information about the pertinent map to receive, in order to be able to merge it.

Were developed the Zorro bus from the CCU expansion plumb bob of the Amiga 1000. Many later extensions of the Amiga 500 (pluses) and the Amiga 1200 were based on it.

"The Zorro 2 "of the Amiga 2000 was appropriate for a data capacity of 16 bits. With the Amiga 3000 this was extended on 32 bits data capacity (Zorro 3), however can further Zorro-2-Karten (16 bits) be used.

The Amiga 4000 uses same Zorro-3-Slots as the Amiga the 3000.

Extension cards for the Zorro bus offered beside Commodore themselves also to Great Valley Products, phase5 and some other third offerers.

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