lc3_microinstruction - LC-3 microinstruction (signals not...

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Unformatted text preview: LC-3 microinstruction (signals not used in ECE 290 omitted) microsequencing bits in the LC-3 microinstruction - bits [48:39] Signal Description IRD COND J = 1, CAR = 0, CAR 00||opcode (opcode = IR[15:12]), only during decode J (plus 1,2,4,8,16 depending on COND bits) = 000, CAR J = 001, IF (R=1 and J[1]=0) THEN (CAR = 010, IF (BEN=1 and J[2]=0) THEN (CAR = 011, IF (IR[11]=1 and J[0]=0) THEN (CAR J plus 2) ELSE (CAR J plus 4) ELSE (CAR J plus 1) ELSE (CAR J) J) J) 6-bit next value for CAR (plus modifications depending on COND bits) control word bits in the LC-3 microinstruction - bits [38:0] (signals not used in ECE 290 omitted) Signal LD.MAR LD.MDR LD.IR LD.PC LD.REG LD.BEN Description = 1, MAR is loaded = 1, MDR is loaded = 1, IR is loaded = 1, PC is loaded = 1, register file is loaded = 1, updates Branch Enable (BEN) bit Signal Description LD.CC GateMARMUX GateMDR GateALU GatePC = 0, chooses ZEXT IR[7:0] MARMUX MIO.EN = 1, chooses address adder output ADDR1MUX = 0, chooses PC = 1, chooses reg file SR1OUT ADDR2MUX = 00, chooses "0...00" = 01, chooses SEXT IR[5:0] = 10, chooses SEXT IR[8:0] = 11, chooses SEXT IR[10:0] PCMUX SR1MUX = 00, chooses PC + 1 = 01, chooses system bus = 10. chooses address adder output = 00, chooses IR[11:9] = 01, chooses IR[8:6] = 10, chooses "110" R.W ALUK DRMUX = 1, updates status bits from system bus = 1, MARMUX output is put onto system bus = 1, MDR contents are put onto system bus = 1, ALU output is put onto system bus = 1, PC contents are put onto system bus = 1, Enables memory, chooses memory output for MDR input = 0, Disables memory, chooses system bus for MDR input = 1, M[MAR]<-MDR when MIO.EN = 1 = 0, MDR<-M[MAR] when MIO.EN = 1 = 00, ADD = 01, AND = 10, NOT A = 11, PASS A = 00, chooses IR[11:9] = 01, chooses "111" = 10, chooses "110" ...
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This note was uploaded on 06/21/2011 for the course ECE 290 taught by Professor Staff during the Spring '08 term at University of Illinois, Urbana Champaign.

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