Application-Specific Integrated Circuit (ASIC)
An ASIC is an especially manufactured custom Chip designed to fulfill special fonctions.
The main reason is to perform special tasks or combine different electronic componnents into a single Integrated Circuit (Chip).
Amstrad Custom chips
The Amstrad CPC used one custom chip : the video Gate Array (also called VGA...but nothing to share with the Video PC standard...)
Latter CPC cost down series included a "pre-ASIC" to merge the VGA and the CRTC.
The Amstrad Plus include a "second heart" simply referred as the ASIC.
CPC+ ASIC's part number is 40489
This Amstrad Plus ASIC perform many additionnal features that the old CPC series couldn't : the "Plus Features".
Known Flaws
The Asmtrad Plus ASIC improve a lot of old CPC capability. Yet this was a bit flawed.
- Despite removing some tasks from the CPU (Z80), the ASIC had to use specific central memory addresses, so "took away" this memory from the CPU...
Not that important for a 64Ko Ram system (464+ and GX4000) yet this is a serious limitation when dealing with Extra memory (6128+ and Extra Ram peripheral)
- There's a DMA bug (Help needed).
- Some argue that the Asic simply badly Emulates an old CPC, but it is not really one. The Colours are slightly different and some softwares (games) couldn't work until modified (Addons for such Old CPC games often exist now).
As a result, some people say that the Plus is not a CPC...