Commodore
Amiga 2000B

Early prototype of a CR 2000 (West Chester model)

This is something rather special, it's a rev 3.9 CR board. This is a pre production model of which only 200 were made. It is plagued with small errors that were corrected later in the rev 4.x CR board. Dave Haynie, developer of the Amiga 2000CR has this to say about the rev 3.9: About 200 pre-production B2000s were released, as "Dealer Demo" units, never meant to be sold. That's labelled Rev 3.9, of course some dealers sold them, since the A2000 was hot. These may have problems with CPU slot devices since, like the orginal A2000, there was no additional buffering on the clocks that drove that slot (and timing is very critical in many CPU slot applications). This board includes the Buster "Tower". That tower's my fault, let me explain. When I took over the Amiga 2000 project, in the fall of 1986 (well, after the shock wore off), I set out to implement the first "Buster" (Bus controller) chip. This did with the expansion logic much of what Gary and the Fat Agnus did to the original Amiga 1000 logic: shrunk it in price and in size. Since I was, in essence, copying the German design (they _do_ look similar, eh), I took the PAL equations from the Amiga 2000 on the left as my basis for the Buster chip. Whoops. There was a bug in the German PALs. There are a set of buffers between the A2000's local bus (directly on the 68000) and the Zorro bus. When a Zorro bus master talks to a Zorro bus target, these buffers are supposed to point away from Zorro, toward the local bus. During pre-production testing at the Commodore plant in Taiwan, I discovered that wasn't the case with the German A2000, or my shiny new Buster chip -- motherboard buffers fought with anything driving the expansion bus in this case. Whoops. In Germany, they fixed it with a new PAL. The Buster "tower" fixed it here, until a corrected Buster chip could be produced.