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ASIC
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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==
*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.
==External Links==
*[http://en.wikipedia.org/wiki/Application-specific_integrated_circuit ASIC at Wikipedia]General information on ASICs.
*[http://www.cpctech.org.uk/docs/arn5new.html Asic and Plus features at Unofficial CPC ressources 1.4]
*[http://www.cpctech.org.uk/docs/arnold5a.html Asic and Plus features at Unofficial CPC ressources 1.5]
*[http://www.cpctech.org.uk/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:Electronic Component]][[Category:Programming]][[Category:Datasheet]][[Category:Graphic]]
[[Category:Stub]][[Category:CPC Internal Components]]
