The ASIC (Application Specific Integrated Circuit) was the equivalent of the ULA (Uncommited Logic Array) in the ZX Spectrum, a multi-purpose logic chip to provide functions that would normally require discrete logic chips and hence extra cost.
The ASIC was also responsible for some Hardware Bugs and limitations due to the amount of available pins on the package.
There also exist 40 prototype Golden ASICs, some framed and signed by Bruce Gordon.