The A3000 bus is a rather extensive superset of the A2000 bus design. The compatibility is based on distinct bus modes, rather than a simple extension to the existing bus mechanisms. Through the use of an integrated bus controller (the Fat Buster chip ), the expansion bus configures itself differently for the 16-bit A2000-compatible Zorro II modes than the 32-bit Zorro III modes. As a result, while there are still only 100 pins on the expansion bus, some pins change function considerably depending on the bus activity that's currently in progress. While the Zorro II modes of the Zorro III bus are as compatible as possible with the Zorro II bus specification (especially the A2000 implementation of this specification), there are some small differences between the two expansion buses. Aside from these differences, in general, it's important to understand the Zorro II bus in order to understand the Zorro III bus. The general features of the A3000 bus, like autoconfiguration , the master-slave bus architecture, and the physical attributes come from the Zorro II expansion bus. Other features of the Zorro III bus address shortcomings of the Zorro II architecture, but Zorro II has a hand in how some of these shortcomings are solved under Zorro III. Those with a full understanding of the Zorro II bus will mainly be concerned with the possible bus incompatibilities listed here. Changes from the A2000 Bus Signal Description Zorro II Bus Architecture
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