send.tdf

在QuartusII中使用AHDL语言编写一个RS232串行数据通信接口

% ***** Clock frequency is 3.456 MHz ***** %
% ***** Clock period is 289.35 ns ***** %
% ***** Data rate is 14,400 bps ***** %
% ***** Dataout period is 69.44 us ***** %
subdesign RS2321
(
	%clock          				:Input;%
	dataoutset,dataoutclk					:input;
	data_to_urst					:output;
	Cpudata[7..0]				:input;
	outRegister[8..0]           :output;
	dataoutCounter[3..0]		:output;
	SendCountReset				:output;
	sending						:input;
)
Variable
	outRegister[8..0]           :dff;
	dataoutCounter[3..0]		:dff;
	SendCountReset				:dff;
begin
	%set clock%
	outRegister[8..0].clk=dataoutclk;
	dataoutCounter[3..0].clk=dataoutclk;
	SendCountReset.clk=dataoutclk;
		
	% send data to recieve machine%          		
	if (sending==1) then 	
		if (dataoutset==1) then
			outRegister[8..1].d=Cpudata[7..0];
			outRegister[0].d=vcc;
		else outRegister[7..0].d=outRegister[8..1].q;
		outRegister[8].d=gnd;
		
		end if;
		
		data_to_urst=outRegister[0].q;
		
		dataoutCounter[3..0].d=(dataoutCounter[3..0].q+1)&!SendCountReset;
		Case dataoutCounter[] is
                    WHEN H"8" =>
                        SendCountReset.d=Vcc;
                    WHEN OTHERS =>
                        SendCountReset.d=Gnd;
     	End Case;	
	 
	end if;	
	
	end;