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// borrowed with some modifications from
// http://www.ee.ed.ac.uk/~gerard/Teach/Verilog/manual/Example/lrgeEx2/cooley.html
module up3down5(clock, data_in, up, down, carry_out, borrow_out, count_out, parity_out);
input [8:0] data_in;
input clock, up, down;
output reg [8:0] count_out;
output reg carry_out, borrow_out, parity_out;
reg [9:0] cnt_up, cnt_dn;
reg [8:0] count_nxt;
always @(posedge clock)
begin
cnt_dn = count_out - 3'b 101;
cnt_up = count_out + 2'b 11;
case ({up,down})
2'b 00 : count_nxt = data_in;
2'b 01 : count_nxt = cnt_dn;
2'b 10 : count_nxt = cnt_up;
2'b 11 : count_nxt = count_out;
default : count_nxt = 9'bX;
endcase
parity_out <= ^count_nxt;
carry_out <= up & cnt_up[9];
borrow_out <= down & cnt_dn[9];
count_out <= count_nxt;
end
endmodule
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