Apple-II_MiSTer/sys/sigma_delta_dac.v
2017-11-04 21:21:27 +08:00

34 lines
934 B
Verilog

//
// PWM DAC
//
// MSBI is the highest bit number. NOT amount of bits!
//
module sigma_delta_dac #(parameter MSBI=7, parameter INV=1'b1)
(
output reg DACout, //Average Output feeding analog lowpass
input [MSBI:0] DACin, //DAC input (excess 2**MSBI)
input CLK,
input RESET
);
reg [MSBI+2:0] DeltaAdder; //Output of Delta Adder
reg [MSBI+2:0] SigmaAdder; //Output of Sigma Adder
reg [MSBI+2:0] SigmaLatch; //Latches output of Sigma Adder
reg [MSBI+2:0] DeltaB; //B input of Delta Adder
always @(*) DeltaB = {SigmaLatch[MSBI+2], SigmaLatch[MSBI+2]} << (MSBI+1);
always @(*) DeltaAdder = DACin + DeltaB;
always @(*) SigmaAdder = DeltaAdder + SigmaLatch;
always @(posedge CLK or posedge RESET) begin
if(RESET) begin
SigmaLatch <= 1'b1 << (MSBI+1);
DACout <= INV;
end else begin
SigmaLatch <= SigmaAdder;
DACout <= SigmaLatch[MSBI+2] ^ INV;
end
end
endmodule