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

An '''ASIC ''' is an especially manufactured custom Chip chip designed to fulfill special fonctionsfunctions.

The main reason is to perform special tasks or combine different electronic componnents components into a single Integrated Circuit (Chipchip). 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).

The Amstrad CPC used one custom chip : the video [[Gate Array]] (also called VGA...but nothing to share – no connection with the Video PC standard)...)

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

The Amstrad [[Plus]] include included a "second heart" simply referred as the ASIC.

==Emulated chips== 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 additionnal 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 Scrollings.Screen splitting *Maybe some interactions with the ACID chip in Cartridges.Programmable and vectorised interrupts*DMA sound channels.*Many many more.Specific ROM switching

The Asmtrad Amstrad Plus ASIC improve improved a lot of the old CPC 's capability.

*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(RAM or ROM). That means this memory range is not accessible when ASIC registers are paged. *PPI emulation is not correct as the original 8255 does not need validation. On ASIC emulation, this validation is needed so took away some programs written for "old CPCs" will not be able to get keyboard state. *Z80 IM2 mode is bugged. In this memory mode, the Z80 I register gives the high word for vector table. ASIC gives the low word from IVR and the CPUdevices that generate interrupt (raster 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. *There is a conflict between programmable interrupts and some CRTC settings (line screen split). That will cause the RAM refresh to stop and the memory content will be quickly corrupted causing machine crash. *Reducing horizontal blanking could cause another internal conflict when using DMA lists. In the worst case, this conflict can cause irreversible damage to the ASIC. *Original CPC colors emulation is not correct. ==Internal Links==

*There's a DMA bug (Help needed).[[CRTC]]*[[Gate Array]]

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

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