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ASIC
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'''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).
==Amstrad Custom chips==
The Amstrad CPC used one custom chip: the video [[Gate Array]] (also called VGA – 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]] included a "second heart" simply referred as the ASIC.
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==
Yet this was a bit flawed.
*Despite removing some tasks from the CPU ([[Z80]]), ASIC registers are mapped onto memory from #4000 to #7FFF range prior to other type of memory (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 some programs written for "old CPCs" will not be able to get keyboard state.
*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 (raster and DMAs channels).ASIC generates sometimes may generate a bad values and the raster interrupt routine is called instead of DMA0 routine.The reasons if the Z80 is running particular portions of this bug are not knownmemory. 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 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.
*[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]
[[Category:CPC Plus|*]][[Category:HardwareElectronic Component]][[Category:Programming]][[Category:Datasheet]][[Category:Graphic]]
[[Category:Stub]][[Category:CPC Internal Components]]
