Warp-SE/cpld/CS.v
Zane Kaminski 9a9838a2c2 idk
2023-04-07 06:38:37 -04:00

61 lines
2.1 KiB
Verilog

module CS(
/* MC68HC000 interface */
input [23:08] A, input CLK, input nRES, input nWE,
/* AS cycle detection */
input BACT,
/* Device select outputs */
output IOCS, output IOPWCS, output IACS,
output ROMCS, output ROMCS4X,
output RAMCS, output RAMCS0X, output SndRAMCSWR);
/* Overlay control */
reg nOverlay = 0; wire Overlay = !nOverlay;
reg ODCSr;
always @(posedge CLK) begin
ODCSr <= ROMCS4X && BACT;
if (!BACT) begin
if (!nRES) nOverlay <= 0;
else if (ODCSr) nOverlay <= 1;
end
end
/* ROM select signals */
assign ROMCS4X = A[23:20]==4'h4;
assign ROMCS = ((A[23:20]==4'h0) && Overlay) || ROMCS4X;
/* RAM select signals */
assign RAMCS0X = A[23:22]==2'b00;
assign RAMCS = RAMCS0X && !Overlay;
wire VidRAMCSWR64k = RAMCS && !nWE && (A[23:20]==4'h3) && (A[19:16]==4'hF); // 3F0000-3FFFFF
wire VidRAMCSWR = VidRAMCSWR64k && (
(A[15:12]==4'h2) || // 1792 bytes RAM, 2304 bytes video
(A[15:12]==4'h3) || // 4096 bytes video
(A[15:12]==4'h4) || // 4096 bytes video
(A[15:12]==4'h5) || // 4096 bytes video
(A[15:12]==4'h6) || // 4096 bytes video
(A[15:12]==4'h7) || // 3200 bytes video, 896 bytes RAM,
(A[15:12]==4'hA) || // 256 bytes RAM, 768 bytes sound, 768 bytes RAM, 2304 bytes video
(A[15:12]==4'hB) || // 4096 bytes video
(A[15:12]==4'hC) || // 4096 bytes video
(A[15:12]==4'hD) || // 4096 bytes video
(A[15:12]==4'hE) || // 4096 bytes video
(A[15:12]==4'hF)); // 3200 bytes video, 128 bytes RAM (system error space), 768 bytes sound
/* Select signals - IOB domain */
assign IACS = (A[23:20]==4'hF) && (A[19:18]==2'b11); // IACK
assign IOCS = (A[23:20]==4'hF) || // IACK
(A[23:20]==4'hE) || // VIA
(A[23:20]==4'hD) || // IWM
(A[23:20]==4'hC) || // empty / fast ROM
(A[23:20]==4'hB) || // SCC write
(A[23:20]==4'hA) || // empty
(A[23:20]==4'h9) || // SCC read/reset
(A[23:20]==4'h8) || // empty
(A[23:20]==4'h7) || // empty
(A[23:20]==4'h6) || // empty
(A[23:20]==4'h5) || // SCSI
((A[23:20]==4'h4) && Overlay) ||
VidRAMCSWR; // ROM once
assign IOPWCS = VidRAMCSWR;
endmodule