Changes

'''Application-Specific Integrated Circuit ''' (ASIC)

An '''ASIC ''' is an especially manufactured custom chip designed to fulfil fulfill special functions.

The main reason is to perform special tasks or combine different electronic components into a single Integrated Circuit (chip). This chip is not commonly available ([[COTS]]), but has to be ordered as a genuine part, prices dictated by the seller. After a seller goes out of business or stops supporting a product line, before IPs (Instruction set Processors) like [[CPLD]] or [[FPGA]], they essentially became unavailable. [[Commodore_64#ICs|Commodore]] used a plethora of ASICs in their machines (VIC, SID, PAULA,......); [[MSX]] or the [[IBM PC]]/XT/AT were the opposite in using only [[COTS]] components, making it easy for third parties to offer parts (or to re-build and repair the computers for as long as the COTS chip was still available or a backwards-compatible component exists).

Latter [[CPC]] cost down series included a "pre-ASIC" -called ASIC to merge the VGA and the [[CRTC]].

CPC+ ASIC emulates the following chips : * [[CRTC]] 6845* [[Gate Array]]* [[PAL16L8|PAL]] (128K RAM paging)* [[8255 PPI]]* Printer Port Data and Strobe* Floppy Motor enable [[flip-flop]], Floppy Address decoding (FDC chip Select) ==New features== This Amstrad Plus ASIC perform performs many additional features that the old CPC series couldn't: the "Plus Features".

*[[Soft scrolling (in complement with register 12&13 of the CRTC]] emulation.)*Hardware Scrolling.Screen splitting *Maybe some interactions with the [[Amstrad Cartridge Identification Device|ACID]] chip in cartridges.Programmable and vectorised interrupts*DMA sound channels.*Many many more.Specific ROM switching

*Despite removing some tasks from the CPU ([[Z80]]), the ASIC had registers are mapped onto memory from #4000 to use specific central #7FFF range prior to other type of memory addresses, so "took away" (RAM or ROM). That means this memory from the CPU..range is not accessible when ASIC registers are paged.

This was *PPI emulation is not that important for a 64KB RAM system (464+ and GX4000) yet correct as the original 8255 does not need validation. On ASIC emulation, this validation is a serious limitation when dealing with Extra memory (6128+ and Extra RAM peripheral)needed so some programs written for "old CPCs" will not be able to get keyboard state.

*There's a DMA bug Z80 IM2 mode is bugged. In this mode, the Z80 I register gives the high word for vector table. ASIC gives the low word from IVR and the devices that generate interrupt (Help neededraster and DMAs channels). ASIC may generate a bad values and the raster interrupt routine is called instead of DMA0 routine if the Z80 is running particular portions of memory. See [[Plus Vectored Interrupt Bug]] for more details.

*Some argue that the ASIC simply badly emulates an old CPC, but it There is not really one. The colours are slightly different a conflict between programmable interrupts and some software CRTC settings (games) couldn't work until modified (patches for such old CPC games often exist nowline screen split). That will cause the RAM refresh to stop and the memory content will be quickly corrupted causing machine crash.

As a result, some people say that the Plus *Original CPC colors emulation is not a CPCcorrect. 

*[http://en.wikipedia.org/wiki/Application-specific_integrated_circuit ASIC at Wikipedia]General information on ASICs. 

*[http://www.kjthackercpctech.f2sorg.comuk/docs/arn5new.html Asic and Plus features at Unofficial CPC ressources 1.4]*[http://www.kjthackercpctech.f2sorg.comuk/docs/arnold5a.html Asic and Plus features at Unofficial CPC ressources 1.5]*[http://www.kjthackercpctech.f2sorg.comuk/docs/cpcplus.html Extra Plus Hardware Information]*[http://quasar.cpcscene.net/doku.php?id=assem:asic Quasar ASIC documentation (in french)]

[[Category:CPC Plus|*]][[Category:HardwareElectronic Component]][[Category:Programming]][[Category:Datasheet]][[Category:Graphic]][[Category:Stub]][[Category:Built in HardwareCPC Internal Components]]