PIC單片機(jī)的I2C應(yīng)用程序1

PIC單片機(jī)的I2C應(yīng)用程序1File:an734.asmFunctionality:;ThiscodeimplementsthebasicfunctionsforanI2CslavedeviceusingtheSSPmodule.AllI2CfunctionsarehandledinanISR.Byteswrittentotheslavearestoredinabuffer.Afteranumberofbyteshavebeenwritten,themasterdevicecanthenreadthebytesbackfromthebuffer.;VariablesandConstantsusedintheprogram:Thestartaddressforthereceivebufferisstoredinthevariable'RXBuffer'.Thelengthofthebufferisdenotedbytheconstantvalue'RX_BUF_LEN'.Thecurrentbufferindexisstoredinthevariable'Index'.;;--------------------------------------------------------------------;ThefollowingfilesshouldbeincludedintheMPLABproject:;an734.asm--Mainsourcecodefile;;16f872.lkr--Linkerscriptfile(changethisfileforthedeviceyouareusing);---------------------------------------------------------------------#include<p16f872.inc>;Changetodevicethatyouareusing.;---------------------------------------------------------------------;ConstantDefinitions;---------------------------------------------------------------------#defineNODE_ADDR0x02;I2CaddressofthisnodeChangethisvaluetoaddressthatyouwishtouse.;---------------------------------------------------------------------;BufferLengthDefinition;---------------------------------------------------------------------#defineRX_BUF_LEN32;Lengthofreceivebuffer;---------------------------------------------------------------------;Variabledeclarations;---------------------------------------------------------------------udataWREGsaveres1STATUSsaveres1FSRsaveres1PCLATHsaveres1Indexres1;IndextoreceivebufferTempres1;RXBufferresRX_BUF_LEN;Holdsrec'dbytesfrommaster;device.;---------------------------------------------------------------------;Vectors;---------------------------------------------------------------------STARTUPcodenopgotoStartup;nop;0x0002nop;0x0003gotoISR;0x0004PROGcode;---------------------------------------------------------------------;Macros;---------------------------------------------------------------------memsetmacroBuf_addr,Value,LengthmovlwLength;ThismacroloadsarangeofdatamemorymovwfTemp;withaspecifiedvalue.ThestartingmovlwBuf_addr;addressandnumberofbytesarealsomovwfFSR;specified.SetNextmovlwValuemovwfINDFincfFSR,FdecfszTemp,FgotoSetNextendmLFSRmacroAddress,Offset;ThismacroloadsthecorrectvaluemovlwAddress;intotheFSRgivenaninitialdatamovwfFSR;memoryaddressandoffsetvalue.movfOffset,WaddwfFSR,Fendm;---------------------------------------------------------------------;MainCode;---------------------------------------------------------------------StartupbcfSTATUS,RP1bsfSTATUS,RP0callSetupMainclrwdt;CleartheWDTgotoMain;Loopforever.;---------------------------------------------------------------------;InterruptCode;---------------------------------------------------------------------ISRmovwfWREGsave;SaveWREGmovfSTATUS,W;GetSTATUSregisterbankselSTATUSsave;Switchbanks,ifneeded.movwfSTATUSsave;SavetheSTATUSregistermovfPCLATH,W;movwfPCLATHsave;SavePCLATHmovfFSR,W;movwfFSRsave;SaveFSRbankselPIR1btfssPIR1,SSPIF;IsthisaSSPinterrupt?goto$;No,justtraphere.bcfPIR1,SSPIFcallSSP_Handler;Yes,serviceSSPinterrupt.bankselFSRsavemovfFSRsave,W;movwfFSR;RestoreFSRmovfPCLATHsave,W;movwfPCLATH;RestorePCLATHmovfSTATUSsave,W;movwfSTATUS;RestoreSTATUSswapfWREGsave,F;swapfWREGsave,W;RestoreWREGretfie;Returnfrominterrupt.;---------------------------------------------------------------------Setup;Initializesprogramvariablesandperipheralregisters.;---------------------------------------------------------------------bankselPCONbsfPCON,NOT_PORbsfPCON,NOT_BORbankselIndex;ClearvariousprogramvariablesclrfIndexclrfPORTBclrfPIR1bankselTRISBclrfTRISBmovlw0x36;SetupSSPmodulefor7-bitbankselSSPCONmovwfSSPCON;address,slavemodemovlwNODE_ADDRbankselSSPADDmovwfSSPADDclrfSSPSTATbankselPIE1;EnableinterruptsbsfPIE1,SSPIEbsfINTCON,PEIE;EnableallperipheralinterruptsbsfINTCON,GIE;EnableglobalinterruptsbcfSTATUS,RP0return;---------------------------------------------------------------------SSP_Handler;---------------------------------------------------------------------;TheI2Ccodebelowchecksfor5states:;---------------------------------------------------------------------State1:I2Cwriteoperation,lastbytewasanaddressbyte.SSPSTATbits:S=1,D_A=0,R_W=0,BF=1;State2:I2Cwriteoperation,lastbytewasadatabyte.SSPSTATbits:S=1,D_A=1,R_W=0,BF=1;State3:I2Creadoperation,lastbytewasanaddressbyte.SSPSTATbits:S=1,D_A=0,R_W=1,BF=0;State4:I2Creadoperation,lastbytewasadatabyte.SSPSTATbits:S=1,D_A=1,R_W=1,BF=0;State5:SlaveI2ClogicresetbyNACKfrommaster.SSPSTATbits:S=1,D_A=1,R_W=0,BF=0;Forconvenience,WriteI2CandReadI2Cfunctionshavebeenused.;----------------------------------------------------------------------bankselSSPSTATmovfSSPSTAT,W;GetthevalueofSSPSTATandlwb'00101101';MaskoutunimportantbitsinSSPSTAT.bankselTemp;PutmaskedvalueinTempmovwfTemp;forcomparisionchecking.State1:;Writeoperation,lastbytewasanmovlwb'00001001';address,bufferisfull.xorwfTemp,W;btfssSTATUS,Z;AreweinState1?gotoState2;No,checkfornextstate.....memsetRXBuffer,0,RX_BUF_LEN;Clearthereceivebuffer.clrfIndex;Clearthebufferindex.callReadI2C;DoadummyreadoftheSSPBUF.returnState2:;Writeoperation,lastbytewasdata,movlwb'00101001';bufferisfull.xorwfTemp,WbtfssSTATUS,Z;AreweinState2?gotoState3;No,checkfornextstate.....LFSRRXBuffer,Index;Pointtothebuffer.callReadI2C;GetthebytefromtheSSP.movwfINDF;Putitinthebuffer.incfIndex,F;Incrementthebufferpointer.movfIndex,W;Getthecurrentbufferindex.sublwRX_BUF_LEN;Subtractthebufferlength.btfscSTATUS,Z;Hastheindexexceededthebufferlength?clrfIndex;Yes,clearthebufferindex.returnState3:;Readoperation,lastbytewasanmovlwb'00001100';address,bufferisempty.xorwfTemp,WbtfssSTATUS,Z;AreweinState3?gotoState4;No,checkfornextstate.....clrfIndex;Clearthebufferindex.LFSRRXBuffer,Index;PointtothebuffermovfINDF,W;Getthebytefrombuffer.callWriteI2C;WritethebytetoSSPBUFincfIndex,F;Incrementthebufferindex.returnState4:;Readoperation,lastbytewasdata,movlwb'00101100';bufferisempty.xorwfTemp,WbtfssSTATUS,Z;AreweinState4?gotoState5;No,checkfornextstate....movfIndex,W;Getthecurrentbufferindex.sublwRX_BUF_LEN;Subtractthebufferlength.btfscSTATUS,Z;Hastheindexexceededthebufferlength?clrfIndex;Yes,clearthebufferindex.LFSRRXBuffer,Index;PointtothebuffermovfINDF,W;GetthebytecallWriteI2C;WritetoSSPBUFincfIndex,F;Incrementthebufferindex.returnState5:movlwb'00101000';ANACKwasreceivedwhentransmittingxorwfTemp,W;databackfromthemaster.SlavelogicbtfssSTATUS,Z;isresetinthiscase.R_W=0,D_A=1gotoI2CErr;andBF=0return;Ifwearen抰inState5,thensomethingis;wrong.I2CErrno