Hi
I've been coding a rs-232 rx/tx module. after some hardwork, it's all working fine for timeing and everything (rx/tx) -- except one thing-- whenever I reprogram the FPGA, the first byte received always has 0x80 bigger than what was actually sent. everything works fine afterward. I'm using comDebug.
I don't use flow control, and only RXD,TXD lines.
Any suggestion? Thanks.
What does in mean *the first bite received*? After what? If after power-on the revise async resets in appropriate process. If all the bytes are ORed with '1' then you catch the stop bit. Please remember two things when programming rs232: - sample bits at the middle of bit slice; and - pass to receiving next bit at the middle of stop bit.
Do you use an "async_rst" signal to reset the FPGA after configuration?
If not, be careful as the registers start at "0" regardless of the input levels.
Could you share your code so that we can take a look? You can also find some sample code here
Jean
There is no buffer right now, so it cannot receive continuous bytes. working on that when I got this "first byte" problem figured out.
`define LENGTH (50000000/38400) module top2(clk,RXD,TXD,led0,led1); input clk; input RXD; output TXD,led0,led1;
reg [1:0] s1;
reg [7:0] char_w; wire [7:0] char_r; reg go_r,go_w; send qq1 (clk,char_w,go_w,ok_w,TXD); recv qq2 (clk,char_r,go_r,ok_r,RXD); assign led0=~char_w[6]; assign led1=~char_w[7];
always @(posedge clk) begin case (s1) 0: begin s1
Hi
did I mention that a Maxim MAX3386E RS232 voltage converter was between fpga and the connector on my board. maybe it has something to do with it.
also, after some debugging. I found out a few facts:
so from this I can conclude there is something wrong in both the send and recv modules -- for the first byte. strangely every byte afterward is OK.
When I was debugging my modules I did it separately. Send a stream out of UART, make sure it is working prperly. Make sure that receiver is working by observing debug pins on PLD. Revise quartz rate and divider.
Do you synchronize Rx input? I don't and everything working OK; however, there are multibit counters depending on the input, thus I think it should.
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