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/zx_ula/trunk/fpga_version/rtl/ula_with_timex_hicolor_support.v
0,0 → 1,342
`timescale 1ns / 1ps
//////////////////////////////////////////////////////////////////////////////////
// Company: Dept. Architecture and Computing Technology. University of Seville
// Engineer: Miguel Angel Rodriguez Jodar. rodriguj@atc.us.es
//
// Create Date: 19:13:39 4-Apr-2012
// Design Name: ZX Spectrum
// Module Name: ula
// Project Name:
// Target Devices:
// Tool versions:
// Description:
//
// Dependencies:
//
// Revision:
// Revision 1.00 - File Created
// Additional Comments: GPL License policies apply to the contents of this file.
//
//////////////////////////////////////////////////////////////////////////////////
 
`define cyclestart(a,b) ((a)==(b))
`define cycleend(a,b) ((a)==(b+1))
 
module ula(
input clk14, // 14MHz master clock
input reset, // to reset the ULA to normal color mode.
// CPU interfacing
input [15:0] a, // Address bus from CPU (not all lines are used)
input [7:0] din, // Input data bus from CPU
output [7:0] dout, // Output data bus to CPU
input mreq_n, // MREQ from CPU
input iorq_n, // IORQ from CPU
input rd_n, // RD from CPU
input wr_n, // WR from CPU
input rfsh_n, // RFSH from CPU
output clkcpu, // CLK to CPU
output msk_int_n, // Vertical retrace interrupt, to CPU
// VRAM interfacing
output [13:0] va, // Address bus to VRAM (16K)
input [7:0] vramdout,// Data from VRAM to ULA/CPU
output [7:0] vramdin,// Data from CPU to VRAM
output vramoe, //
output vramcs, // Control signals for VRAM
output vramwe, //
// ULA I/O
input ear, //
output mic, // I/O ports
output spk, //
output [7:0] kbrows, // Keyboard rows
input [4:0] kbcolumns, // Keyboard columns
// Video output
output r, //
output g, // RGB TTL signal
output b, // with separate bright
output i, // and composite sync
output csync //
);
 
reg [2:0] BorderColor = 3'b100;
reg TimexHiColorMode = 0;
 
// Pixel clock
reg clk7 = 0;
always @(posedge clk14)
clk7 <= !clk7;
// Horizontal counter
reg [8:0] hc = 0;
always @(posedge clk7) begin
if (hc==447)
hc <= 0;
else
hc <= hc + 1;
end
// Vertical counter
reg [8:0] vc = 0;
always @(posedge clk7) begin
if (hc==447) begin
if (vc == 311)
vc <= 0;
else
vc <= vc + 1;
end
end
// HBlank generation
reg HBlank_n = 1;
always @(negedge clk7) begin
if (`cyclestart(hc,320))
HBlank_n <= 0;
else if (`cycleend(hc,415))
HBlank_n <= 1;
end
 
// HSync generation (6C ULA version)
reg HSync_n = 1;
always @(negedge clk7) begin
if (`cyclestart(hc,344))
HSync_n <= 0;
else if (`cycleend(hc,375))
HSync_n <= 1;
end
 
// VBlank generation
reg VBlank_n = 1;
always @(negedge clk7) begin
if (`cyclestart(vc,248))
VBlank_n <= 0;
else if (`cycleend(vc,255))
VBlank_n <= 1;
end
// VSync generation (PAL)
reg VSync_n = 1;
always @(negedge clk7) begin
if (`cyclestart(vc,248))
VSync_n <= 0;
else if (`cycleend(vc,251))
VSync_n <= 1;
end
// INT generation
reg INT_n = 1;
assign msk_int_n = INT_n;
always @(negedge clk7) begin
if (`cyclestart(vc,248) && `cyclestart(hc,0))
INT_n <= 0;
else if (`cyclestart(vc,248) && `cycleend(hc,31))
INT_n <= 1;
end
 
// Border control signal (=0 when we're not displaying paper/ink pixels)
reg Border_n = 1;
always @(negedge clk7) begin
if ( (vc[7] & vc[6]) | vc[8] | hc[8])
Border_n <= 0;
else
Border_n <= 1;
end
// VidEN generation (delaying Border 8 clocks)
reg VidEN_n = 1;
always @(negedge clk7) begin
if (hc[3])
VidEN_n <= !Border_n;
end
// DataLatch generation (posedge to capture data from memory)
reg DataLatch_n = 1;
always @(negedge clk7) begin
if (hc[0] & !hc[1] & Border_n & hc[3])
DataLatch_n <= 0;
else
DataLatch_n <= 1;
end
// AttrLatch generation (posedge to capture data from memory)
reg AttrLatch_n = 1;
always @(negedge clk7) begin
if (hc[0] & hc[1] & Border_n & hc[3])
AttrLatch_n <= 0;
else
AttrLatch_n <= 1;
end
 
// SLoad generation (negedge to load shift register)
reg SLoad = 0;
always @(negedge clk7) begin
if (!hc[0] & !hc[1] & hc[2] & !VidEN_n)
SLoad <= 1;
else
SLoad <= 0;
end
// AOLatch generation (negedge to update attr output latch)
reg AOLatch_n = 1;
always @(negedge clk7) begin
if (hc[0] & !hc[1] & hc[2])
AOLatch_n <= 0;
else
AOLatch_n <= 1;
end
 
// First buffer for bitmap
reg [7:0] BitmapReg = 0;
always @(negedge DataLatch_n) begin
BitmapReg <= vramdout;
end
// Shift register (second bitmap register)
reg [7:0] SRegister = 0;
always @(negedge clk7) begin
if (SLoad)
SRegister <= BitmapReg;
else
SRegister <= {SRegister[6:0],1'b0};
end
 
// First buffer for attribute
reg [7:0] AttrReg = 0;
always @(negedge AttrLatch_n) begin
AttrReg <= vramdout;
end
// Second buffer for attribute
reg [7:0] AttrOut = 0;
always @(negedge AOLatch_n) begin
if (!VidEN_n)
AttrOut <= AttrReg;
else
AttrOut <= {2'b00,BorderColor,BorderColor};
end
 
// Flash counter and pixel generation
reg [4:0] FlashCnt = 0;
always @(negedge VSync_n) begin
FlashCnt <= FlashCnt + 1;
end
wire Pixel = SRegister[7] ^ (AttrOut[7] & FlashCnt[4]);
 
// RGB generation
reg rI,rG,rR,rB;
assign r = rR;
assign g = rG;
assign b = rB;
assign i = rI;
always @(*) begin
if (HBlank_n && VBlank_n)
{rI,rG,rR,rB} = (Pixel)? {AttrOut[6],AttrOut[2:0]} : {AttrOut[6],AttrOut[5:3]};
else
{rI,rG,rR,rB} = 4'b0000;
end
//CSync generation
assign csync = HSync_n & VSync_n;
// VRAM address and control line generation
reg [13:0] rVA = 0;
reg rVCS = 0;
reg rVOE = 0;
reg rVWE = 0;
assign va = rVA;
assign vramcs = rVCS;
assign vramoe = rVOE;
assign vramwe = rVWE;
// Latches to hold delayed versions of V and H counters
reg [8:0] v = 0;
reg [8:0] c = 0;
// Address and control line multiplexor ULA/CPU
always @(negedge clk7) begin
if (Border_n && (hc[3:0]==4'b0111 || hc[3:0]==4'b1011)) begin // cycles 7 and 11: load V and C from VC and HC
c <= hc;
v <= vc;
end
end
// Address and control line multiplexor ULA/CPU
always @(*) begin
if (Border_n && (hc[3:0]==4'b1000 || hc[3:0]==4'b1001 || hc[3:0]==4'b1100 || hc[3:0]==4'b1101)) begin // cycles 8 and 12: present display address to VRAM
rVA = {1'b0,v[7:6],v[2:0],v[5:3],c[7:3]}; // (cycles 9 and 13 load display byte)
rVCS = 1;
rVOE = !hc[0];
rVWE = 0;
end
else if (Border_n && (hc[3:0]==4'b1010 || hc[3:0]==4'b1011 || hc[3:0]==4'b1110 || hc[3:0]==4'b1111)) begin // cycles 10 and 14: present attribute address to VRAM
rVA = (TimexHiColorMode)? {1'b1,v[7:6],v[2:0],v[5:3],c[7:3]} : // (cycles 11 and 15 load attr byte).
{4'b0110,v[7:3],c[7:3]}; // Attribute address depends upon the mode selected
rVCS = 1;
rVOE = !hc[0];
rVWE = 0;
end
else if (Border_n && hc[3:0]==4'b0000) begin
rVA = a[13:0];
rVCS = 0;
rVOE = 0;
rVWE = 0;
end
else begin // when VRAM is not in use by ULA, give it to CPU
rVA = a[13:0];
rVCS = !a[15] & a[14] & !mreq_n;
rVOE = !rd_n;
rVWE = !wr_n;
end
end
// CPU contention
reg CPUClk = 0;
assign clkcpu = CPUClk;
reg ioreqtw3 = 0;
reg mreqt23 = 0;
wire ioreq_n = a[0] | iorq_n;
wire Nor1 = (~(a[14] | ~ioreq_n)) |
(~(~a[15] | ~ioreq_n)) |
(~(hc[2] | hc[3])) |
(~Border_n | ~ioreqtw3 | ~CPUClk | ~mreqt23);
wire Nor2 = (~(hc[2] | hc[3])) |
~Border_n |
~CPUClk |
ioreq_n |
~ioreqtw3;
wire CLKContention = ~Nor1 | ~Nor2;
always @(posedge clk7) begin // change clk7 by clk14 for 7MHz CPU clock operation
if (CPUClk && !CLKContention) // if there's no contention, the clock can go low
CPUClk <= 0;
else
CPUClk <= 1;
end
always @(posedge CPUClk) begin
ioreqtw3 <= ioreq_n;
mreqt23 <= mreq_n;
end
// ULA-CPU interface
assign dout = (!a[15] & a[14] & !mreq_n)? vramdout : // CPU reads VRAM through ULA as in the +3, not directly
(!iorq_n & !a[0])? {1'b1,ear,1'b1,kbcolumns} : // CPU reads keyboard and EAR state
(!iorq_n && a[7:0]==8'hFF && !rd_n)? {6'b000000,TimexHiColorMode,1'b0} : // Timex hicolor config port. Only bit 1 is reported.
(Border_n)? AttrReg : // to emulate
8'hFF; // port FF (well, cannot be actually FF anymore)
assign vramdin = din; // The CPU doesn't need to share the memory input data bus with the ULA
assign kbrows = {a[11]? 1'bz : 1'b0, // high impedance or 0, as if diodes were been placed in between
a[10]? 1'bz : 1'b0, // if the keyboard matrix is to be implemented within the FPGA, then
a[9]? 1'bz : 1'b0, // there's no need to do this.
a[12]? 1'bz : 1'b0,
a[13]? 1'bz : 1'b0,
a[8]? 1'bz : 1'b0,
a[14]? 1'bz : 1'b0,
a[15]? 1'bz : 1'b0 };
reg rMic = 0;
reg rSpk = 0;
assign mic = rMic;
assign spk = rSpk;
always @(negedge clk7 or posedge reset) begin
if (reset)
TimexHiColorMode <= 0;
else if (!iorq_n && a[7:0]==8'hFF && !wr_n)
TimexHiColorMode <= din[1];
else if (!iorq_n & !a[0] & !wr_n)
{rSpk,rMic,BorderColor} <= din[5:0];
end
endmodule

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