/* 計數(shù)模塊 */
always @(posedge clk1x or posedge rst or negedge clk1x_enable)
if (rst)
no_bits_sent = 4'b0000 ;
else if (!clk1x_enable)
no_bits_sent = 4'b0000 ;
else
no_bits_sent = no_bits_sent + 1 ;

/* 發(fā)送模塊 */
reg [7:0] tsr ; /*發(fā)送移位寄存器*/
reg parity ; /* 校驗位 */
always @(negedge clk1x or posedge rst)
if (rst)
begin
sdo <= 1'b1 ;
tsre <= 1'b1 ;
parity <= 1'b1 ;
tsr <= 8'b0 ;
end
else
begin
if (no_bits_sent == 4'b0001)
begin
tsr <= tbr ; //將緩沖區(qū)中的數(shù)據(jù)載入到移位寄存器
tsre <= 1'b0 ;
end
/*start bit*/
else if (no_bits_sent == 4'b0010)
begin
sdo <= 1'b0 ;
end
/*Data bits */
else if ((no_bits_sent >= 4'b0011) && (no_bits_sent <= 4'b1010))
begin
tsr[7:1] <= tsr[6:0] ;
sr[0] <= 1'b0 ;
sdo <= tsr[7] ;
parity <= parity ^ tsr[7] ;
end
/* 校驗位 */
else if (no_bits_sent == 4'b1011)
begin
sdo <= parity ;
end
else if (no_bits_sent == 4'b1100)
begin
sdo <= 1'b1 ;
tsre <= 1'b1 ;
end
end