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title: "The Backplane Map: Spectrum vs 2068"
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excerpt: "The following will give you some idea of the differences between the Spectrum expansion bus and the 2068's. This information will help you hack Spectrum hardware onto a 2068. If you've never looked at such things, some of the conventions may be unfamiliar. Names with a bar overhead (such as INT) are read \"not INT\".…"
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# The Backplane Map: Spectrum vs 2068

The following will give you some idea of the differences between the Spectrum expansion bus and the 2068’s.

[![Image](http://localhost/wp-content/uploads/2022/10/spectrum-2068-bus.png)](http://localhost/wp-content/uploads/2022/10/spectrum-2068-bus.png)

This information will help you hack Spectrum hardware onto a 2068. If you’ve never looked at such things, some of the conventions may be unfamiliar. Names with a bar overhead (such as INT) are read “not INT”. It means they are *active low*. In other words, their rest state is +5v; when they do their job, they drop to 0v. The other detail is the “B” after some entries. This indicates a buffered line; rather that just leading the line out from the Z80 chip, additional circuitry has been added to reinforce the signal. Its not changed, but it able to travel farther, or service more other circuits than unbuffered lines.