File size: 1,591 Bytes
8dc19e4 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 | // 8-line to 3-line priority encoder
module ttl_74148 #(parameter WIDTH_IN = 8, WIDTH_OUT = 3, DELAY_RISE = 0, DELAY_FALL = 0)
(
input EI_bar,
input [WIDTH_IN-1:0] A_bar,
output EO_bar,
output GS_bar,
output [WIDTH_OUT-1:0] Y_bar
);
//------------------------------------------------//
reg EO_computed;
reg GS_computed;
reg [WIDTH_OUT-1:0] Y_computed;
always @(*)
begin
if (EI_bar)
begin
// equal to EI (inverted)
EO_computed = 0;
// equal to EI (inverted)
GS_computed = 0;
// lowest priority (inverted)
Y_computed = 3'b000;
end
else
begin
// normally opposite of EI (inverted)
EO_computed = 0;
// normally equal to EI (inverted)
GS_computed = 1;
casez (A_bar)
8'b0???????: Y_computed = 3'b111;
8'b10??????: Y_computed = 3'b110;
8'b110?????: Y_computed = 3'b101;
8'b1110????: Y_computed = 3'b100;
8'b11110???: Y_computed = 3'b011;
8'b111110??: Y_computed = 3'b010;
8'b1111110?: Y_computed = 3'b001;
8'b11111110: Y_computed = 3'b000;
8'b11111111:
begin
// exception: equal to EI (inverted)
EO_computed = 1;
// exception: opposite of EI (inverted)
GS_computed = 0;
// lowest priority (inverted)
Y_computed = 3'b000;
end
default: Y_computed = 3'b000;
endcase
end
end
//------------------------------------------------//
assign #(DELAY_RISE, DELAY_FALL) EO_bar = ~EO_computed;
assign #(DELAY_RISE, DELAY_FALL) GS_bar = ~GS_computed;
assign #(DELAY_RISE, DELAY_FALL) Y_bar = ~Y_computed;
endmodule
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