Programmable Array Logic (PAL). Not to be confused with PAL, the colour encoding system for analog televisions.
The CPC6128 second page of 64KB RAM is controlled by a PAL chip. It has the Amstrad part number 40031.
On the CPC 6128 schematic, it is top centre: [http://www.cpcwiki.eu/imgs/4/4a/CPC6128_Schematic.png CPC6128 Schematic] however the X inputs aren't distinguished.