mirror of
https://github.com/garrettsworkshop/RAM2E.git
synced 2024-11-21 10:33:50 +00:00
474 lines
15 KiB
Verilog
474 lines
15 KiB
Verilog
module RAM2E(C14M, PHI1, LED,
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nWE, nWE80, nEN80, nC07X,
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Ain, Din, Dout, nDOE, Vout, nVOE,
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CKEout, nCSout, nRASout, nCASout, nRWEout,
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BA, RAout, DQML, DQMH, RD);
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/* Clocks */
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input C14M, PHI1;
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/* Control inputs */
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input nWE, nWE80, nEN80, nC07X;
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/* "Fast" (init) state counter */
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reg [15:0] FS = 0; always @(posedge C14M) FS <= FS+16'h0001;
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reg Ready = 0;
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always @(posedge C14M) if (FS[15:0]==16'hFFFF) Ready <= 1'b1;
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/* IIe state counter */
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reg [3:0] S = 0;
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reg PHI1r = 0; always @(posedge C14M) PHI1r <= PHI1;
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always @(posedge C14M) begin
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S <= (PHI1 && !PHI1r && Ready) ? 4'h1 :
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(S==4'h0) ? 4'h0 :
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(S==4'hF) ? 4'hF : S+4'h1;
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end
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/* Refresh counter */
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reg [2:0] RC;
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wire RefReq = RC==0;
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always @(posedge C14M) begin
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if (S==4'h1) begin
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if (RC[2] && RC[1]) RC <= 0; // RC==6 || RC==7
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else RC <= RC+3'h1;
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end
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end
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/* Activity LED */
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wire LEDEN;
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output LED; assign LED = !(!nEN80 && LEDEN && Ready);
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/* Address Bus */
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input [7:0] Ain; // Multiplexed DRAM address input
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/* 6502 Data Bus */
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input [7:0] Din; // 6502 data bus inputs
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reg DOEEN;
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always @(posedge C14M) begin
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DOEEN <= /*(S==4'h8) || (S==4'h9) || (S==4'hA) ||*/ (S==4'hB) ||
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(S==4'hC) || (S==4'hD) || (S==4'hE) || (S==4'hF);
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end
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output nDOE; assign nDOE = !(!nEN80 && nWE && DOEEN);
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output [7:0] Dout; assign Dout[7:0] = RD[7:0];
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/* Video Data Bus */
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reg VOEEN;
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always @(posedge C14M) begin
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VOEEN <= (S==4'h7) ||
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(S==4'h8) || (S==4'h9) || (S==4'hA) || (S==4'hB) ||
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(S==4'hC) || (S==4'hD) || (S==4'hE) || (S==4'hF);
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end
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output nVOE; assign nVOE = !(!PHI1 && VOEEN);
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output reg [7:0] Vout; // Video data bus
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always @(posedge C14M) if (S==4'h6) Vout[7:0] <= RD[7:0];
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/* SDRAM bus */
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reg CKE = 1;
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reg nRAS = 1, nCAS = 1, nRWE = 1;
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output reg [1:0] BA;
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reg [11:0] RA;
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output reg DQML = 1, DQMH = 1;
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inout [7:0] RD;
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wire [7:0] RDout = Ready ? Din[7:0] : 8'h00;
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wire RDOE = (!Ready) || (!nEN80 && !nWE);
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assign RD[7:0] = RDOE ? RDout[7:0] : 8'bZ;
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/* SDRAM falling edge outputs */
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output reg CKEout;
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output nCSout; assign nCSout = 0;
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output reg nRASout = 1, nCASout = 1, nRWEout = 1;
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output reg [11:0] RAout;
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always @(negedge C14M) begin
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CKEout <= CKE;
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nRASout <= nRAS;
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nCASout <= nCAS;
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nRWEout <= nRWE;
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RAout <= RA;
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end
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/* RAMWorks Bank Register and Capacity Mask */
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reg [7:0] RWBank = 0; // RAMWorks bank register
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wire [7:0] RWMask;
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reg RWSel = 0; // RAMWorks bank register select
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always @(posedge C14M) begin
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if (S==4'h9) RWSel <= RA[0] && !RA[3] && !nWE && !nC07X;
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end
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reg CmdRWMaskSet = 0; // RAMWorks Mask register set flag
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wire CmdSetRWBankFFChip;
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reg CmdSetRWBankFFLED = 0;
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reg CmdLEDSet = 0;
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reg CmdLEDGet = 0;
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/* Command Sequence Detector */
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reg [2:0] CS = 0; // Command sequence state
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reg [2:0] CmdTout = 0; // Command sequence timeout
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/* Chip-specific UFM interface */
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RAM2E_UFM ram2e_ufm (
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.C14M(C14M), .S(S), .FS(FS), .CS(CS), .Ready(Ready),
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.RWSel(RWSel), .D(Din),
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.RWMask(RWMask), .LEDEN(LEDEN),
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.CmdRWMaskSet(CmdRWMaskSet), .CmdLEDSet(CmdLEDSet),
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.CmdSetRWBankFFChip(CmdSetRWBankFFChip));
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/* Command sequence control */
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always @(posedge C14M) begin
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if (S==4'hC) begin
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if (RWSel) begin
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CmdTout <= 0; // Reset command timeout if RWSel accessed
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// Recognize command sequence and advance CS state
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if ((CS==3'h0 && Din[7:0]==8'hFF) ||
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(CS==3'h1 && Din[7:0]==8'h00) ||
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(CS==3'h2 && Din[7:0]==8'h55) ||
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(CS==3'h3 && Din[7:0]==8'hAA) ||
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(CS==3'h4 && Din[7:0]==8'hC1) ||
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(CS==3'h5 && Din[7:0]==8'hAD) ||
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CS==3'h6 || CS==3'h7) CS <= CS+3'h1;
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else CS <= 0; // Back to beginning if it's not right
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end else begin
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CmdTout <= CmdTout+3'h1; // Increment command timeout
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// If command sequence times out, reset sequence state
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if (CmdTout==3'h7) CS <= 0;
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end
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end
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end
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/* RAMWorks register control - bank, LED, etc. */
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always @(posedge C14M) begin
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if (S==4'hC && RWSel) begin
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// Latch RAMWorks bank if accessed
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if ((CmdSetRWBankFFLED) || (CmdSetRWBankFFChip) ||
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(CmdLEDGet && LEDEN)) RWBank <= 8'hFF;
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else RWBank <= Din[7:0] & {RWMask[7], ~RWMask[6:0]};
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if (CS==3'h6) begin // Recognize and submit command in CS6
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// LED detect command
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CmdSetRWBankFFLED <= Din[7:0]==8'hF0;
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// Volatile commands
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CmdSetRWBankFFLED <= Din[7:0]==8'hF0;
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CmdRWMaskSet <= Din[7:0]==8'hE0;
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CmdLEDSet <= Din[7:0]==8'hE2;
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CmdLEDGet <= Din[7:0]==8'hE3;
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end else begin // Reset command triggers
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CmdSetRWBankFFLED <= 0;
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CmdRWMaskSet <= 0;
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CmdLEDSet <= 0;
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CmdLEDGet <= 0;
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end
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end
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end
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/* SDRAM Control */
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always @(posedge C14M) case (S)
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4'h0: begin
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CKE <= 1'b1;
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if (!FS[15] || FS[0]) begin
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// NOP
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nRAS <= 1'b1;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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end else case (FS[4:1])
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4'h0: begin
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// PC all
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nRAS <= 1'b0;
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nCAS <= 1'b1;
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nRWE <= 1'b0;
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end 4'h1: begin
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// LDM
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nRAS <= 1'b0;
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nCAS <= 1'b0;
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nRWE <= 1'b0;
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end 4'h2: begin
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// NOP
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nRAS <= 1'b1;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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end 4'h3, 4'h4, 4'h5, 4'h6,
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4'h7, 4'h8, 4'h9, 4'hA: begin
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// AREF
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nRAS <= 1'b0;
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nCAS <= 1'b0;
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nRWE <= 1'b1;
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end 4'hB: begin
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// ACT
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nRAS <= 1'b0;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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end 4'hC, 4'hD: begin
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// WR
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nRAS <= 1'b1;
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nCAS <= 1'b0;
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nRWE <= 1'b0;
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end 4'hE: begin
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// NOP
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nRAS <= 1'b1;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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end 4'hF: begin
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// PC all
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nRAS <= 1'b0;
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nCAS <= 1'b1;
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nRWE <= 1'b0;
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end
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endcase
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case (FS[4:3])
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2'b00, 2'b01: begin
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// Mode register contents
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BA[1:0] <= 2'b00; // Reserved
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RA[11] <= 1'b0; // Reserved
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RA[10] <= !FS[1]; // reserved / "all"
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RA[9] <= 1'b1; // "1" for single write mode
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RA[8] <= 1'b0; // Reserved
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RA[7] <= 1'b0; // "0" for not test mode
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RA[6:4] <= 3'b010; // "2" for CAS latency 2
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RA[3] <= 1'b0; // "0" for sequential burst (not used)
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RA[2:0] <= 3'b000; // "0" for burst length 1 (no burst)
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end 2'b10: begin
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BA[1:0] <= 2'b00;
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RA[11:8] <= 4'h0;
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RA[7:0] <= FS[14:7];
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end 2'b11: begin
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BA[1:0] <= 2'b00;
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RA[11:3] <= 9'h000;
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RA[2:1] <= FS[6:5];
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RA[0] <= FS[1];
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end
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endcase
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DQML <= !FS[15];
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DQMH <= !FS[15];
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end 4'h1: begin
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// NOP CKE
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CKE <= 1'b1;
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nRAS <= 1'b1;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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BA[1:0] <= 2'b00;
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RA[11:8] <= 4'b0000;
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// Hold RA[7:0]
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DQML <= 1'b0;
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DQMH <= 1'b1;
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end 4'h2: begin
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// ACT CKE
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CKE <= 1'b1;
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nRAS <= 1'b0;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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// Hold BA
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// Hold RA
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// Hold DQMs
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end 4'h3: begin
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// RD CKE
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CKE <= 1'b1;
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nRAS <= 1'b1;
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nCAS <= 1'b0;
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nRWE <= 1'b1;
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// Hold BA
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// Hold RA[11:8]
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RA[7:0] <= Ain[7:0];
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// Hold DQMs
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end 4'h4: begin
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if (RefReq) begin // Refresh request
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// PC all CKE
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CKE <= 1'b1;
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nRAS <= 1'b0;
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nCAS <= 1'b1;
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nRWE <= 1'b0;
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end else begin // No refresh request
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// PC all CKD
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CKE <= 1'b0;
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nRAS <= 1'b0;
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nCAS <= 1'b1;
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nRWE <= 1'b0;
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end
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// Hold BA
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// Hold RA[11]
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RA[10] <= 1'b1; // "all"
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// Hold RA[9:0]
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// Hold DQMs
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end 4'h5: begin
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if (RefReq) begin // Refresh request
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// AREF CKE
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CKE <= 1'b1;
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nRAS <= 1'b0;
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nCAS <= 1'b0;
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nRWE <= 1'b1;
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end else begin // No refresh request
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// NOP CKD
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CKE <= 1'b0;
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nRAS <= 1'b1;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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end
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// Hold BA
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// Hold RA
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// Hold DQMs
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end 4'h6: begin
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// NOP CKD
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CKE <= 1'b0;
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nRAS <= 1'b1;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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// Hold BA
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// Hold RA
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// Hold DQMs
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end 4'h7: begin
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// Can't check EN80 at this time
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// NOP CKE
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CKE <= 1'b1;
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nRAS <= 1'b1;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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// Hold BA
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// Hold RA[11:8]
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RA[7:0] <= Ain[7:0];
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// Hold DQMs
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end 4'h8: begin
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if (nEN80) begin // Idle
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// NOP CKD
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CKE <= 1'b0;
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nRAS <= 1'b1;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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end else if (nWE) begin // Read
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// ACT CKE
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CKE <= 1'b1;
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nRAS <= 1'b0;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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end else begin // Write
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// ACT CKD
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CKE <= 1'b0;
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nRAS <= 1'b0;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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end
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BA[1:0] <= RWBank[6:5];
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RA[11:8] <= RWBank[4:1];
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// Hold RA[7:0]
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// Hold DQMs
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end 4'h9: begin
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if (nEN80) begin // Idle
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// NOP CKD
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CKE <= 1'b0;
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nRAS <= 1'b1;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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end else if (nWE) begin // Read
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// RD CKE
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CKE <= 1'b1;
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nRAS <= 1'b1;
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nCAS <= 1'b0;
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nRWE <= 1'b1;
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end else begin // Write
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// NOP CKE
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CKE <= 1'b1;
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nRAS <= 1'b1;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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end
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// Hold BA
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RA[11:9] <= 3'b000; // no auto-precharge
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RA[8] <= RWBank[7];
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RA[7:0] <= Ain[7:0];
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DQML <= RWBank[0];
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DQMH <= !RWBank[0];
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end 4'hA: begin
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if (nEN80) begin // Idle
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// NOP CKD
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CKE <= 1'b0;
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nRAS <= 1'b1;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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RA[10] <= 1'b0;
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end else if (nWE) begin // Read
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// PC all CKD
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CKE <= 1'b0;
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nRAS <= 1'b0;
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nCAS <= 1'b1;
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nRWE <= 1'b0;
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RA[10] <= 1'b1; // "all"
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end else begin // Write
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// WR CKE
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CKE <= 1'b1;
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nRAS <= 1'b1;
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nCAS <= 1'b0;
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nRWE <= 1'b0;
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RA[10] <= 1'b0; // no auto-precharge
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end
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// Hold BA
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// Hold RA[11,9:0]
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// Hold DQMs
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end 4'hB: begin
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if (nEN80) begin // Idle
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// NOP CKD
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CKE <= 1'b0;
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nRAS <= 1'b1;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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end else if (nWE) begin // Read
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// NOP CKD
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CKE <= 1'b0;
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nRAS <= 1'b1;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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end else begin // Write
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// NOP CKE
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CKE <= 1'b1;
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nRAS <= 1'b1;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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end
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// Hold BA
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// Hold RA[11:0]
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// Hold DQMs
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end 4'hC: begin
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if (nEN80) begin // Idle
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// NOP CKD
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CKE <= 1'b0;
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nRAS <= 1'b1;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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RA[10] <= 1'b0;
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end else if (nWE) begin // Read
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// NOP CKD
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CKE <= 1'b0;
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nRAS <= 1'b1;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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RA[10] <= 1'b1;
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end else begin // Write
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// PC all CKD
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CKE <= 1'b0;
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nRAS <= 1'b0;
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nCAS <= 1'b1;
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nRWE <= 1'b0;
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RA[10] <= 1'b1; // "all"
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end
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// Hold BA
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// Hold RA[11,9:0]
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// Hold RA[7:0]
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// Hold DQMs
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end 4'hD: begin
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// NOP CKD
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CKE <= 1'b0;
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nRAS <= 1'b1;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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// Hold BA
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// Hold RA[11:0]
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// Hold DQMs
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end 4'hE, 4'hF: begin
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// NOP CKD
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CKE <= 1'b0;
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nRAS <= 1'b1;
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nCAS <= 1'b1;
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nRWE <= 1'b1;
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// Hold BA
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// Hold RA[11:8]
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RA[7:0] <= Ain[7:0]; // Latch row address for next video read
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// Hold DQMs
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end
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endcase
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endmodule
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