Amiga Zorro II

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

It was first used as a Zorro -I in the Amiga 1000, is still a 16 - bit mode as Zorro II Amiga in 2000 and finally in 32 bit mode (multiplexed ) as a Zorro - III in the Amiga 3000 and higher.

The bus system of the early Amiga models is the so -called Zorro bus with 24 - bit address space - in A500/1000 laterally through a 86 -pin connector, in A2000 Zorro II internally by several 100 -pin slots in the A3000/A4000 Zorro - III with 32- bit address space by several 100 -pin slots, 32 bit has been achieved by multiplexing the signal lines. With an adapter you could run Zorro II cards on an Amiga 500/1000. Of course, ran all Zorro II cards are still on the Zorro III bus, as it was discovered independently on the bus, whether it is a 16 on the map - acted or 32 -bit card.

In the A2000, A3000 and A4000 models, commercially available IBM-compatible ISA expansion card (16 - bit) could be installed, but a so-called bridge card was to additionally necessary, and hard disks were available by special software from the Amiga side.

Auto- config mechanism

The Zorro bus has a so-called auto- config mechanism that allows an automatic integration of expansion cards during system startup. Each Zorro card rather owns an EPROM or PAL block in which all necessary information is included for the auto -config mode.

These are, for example,

  • Manufacturer code: Each developer of Zorro cards received from Commodore and Amiga Technologies assigned a code number, which it can expansion.library recognize his card with the.
  • Product Number: This number can be freely chosen by the manufacturer and is also required for the recognition of the expansion.library.
  • Serial number: It can be freely chosen by the manufacturer and can mean all sorts of things (4 bytes).
  • Type designation and Flags: The information that follows as of Zorro Standard ( II / III), the size of the required address space and much more.

The address space can be 64 KiB to 8 MiB, at Zorro III are also well 16-1024 MiB possible (both in powers of two ). Thus, the system for the card reserved only as much memory as is needed.

With the Amiga 2000 for the first time self-configuring internal interfaces have been introduced. These internal interfaces of the Amiga are comparable to the much younger PCI slots of today's computers.

Each Zorro card has its own number, which depends on the slot in which they inserted. After a reset, all the cards on the so-called signals CFGIN and CFGOUT be queried. Each card is assigned a 64 kilobyte block of information is for Zorro II from $ 00E8xxxx and Zorro III from $ FF00xxxx. Then all the data necessary for the integration of the map are entered in a system list. After the drivers are installed, get on the expansion.library all necessary information on the accompanying map, in order to link them to.


The Zorro bus Many later extensions of the Amiga were developed from the CPU expansion slot of the Amiga 1000. 500 (plus) and the Amiga 1200 based on it.

The " Zorro II" of the Amiga 2000 was designed for a data width of 16 bits. With the Amiga 3000 this was on 32 -bit data width extended ( Zorro III ), but can still Zorro II cards (16 bits) are used.

The Amiga 4000 uses the same Zorro III slots like the Amiga 3,000.

Expansion cards for the Zorro bus offered alongside Commodore itself also Great Valley Products, phase5 and other providers to.

The hardware logic for the bus protocols was in the custom chip "Buster " housed ( except for the Amiga 2000 "A", there discrete GALs were used ). For Zorro III of " FatBuster " was used.

Following the announcement of the PCI specifications Dave Haynie looks at the development of Zorro IV as obsolete.