A31 Aucc B31 HIGH
Most of the extra pins are DMA related. The Aucc/Agnd pins are meant to be smoother voltages then VCC/GND (for use with Audio expansions).
== Amstrad PCW ==
The Amstrad PCW has a 50-pin Expansion port, too. But it's pin-outs are entirely different as on CPC.
* [[Amstrad PCW Expansion Port]]