Serial Interconnect between two Propellers

fbeek

Hello,

i want to connect two propeller chips together over a serial link.

I tried this with the PCFULLDUPLEX serial object and that works gread at 115200 Baud in mode 0.

But there is one thing that i can't understand. When i read a byte with .rxcheck and put this out to my PC over second link i get always 255 out if there is nothing transmitted

repeat
    intercom:=uart[1].rxcheck
    if(intercom > -1)
    uart[0].tx(intercom)

I can filter that with

repeat
    intercom:=uart[1].rxcheck
    if(intercom > -1 AND intercom < 255)
    uart[0].tx(intercom)

But i think this is not the best way.

Can someone give me some help for this Problem.

fbeek

Luis Digital

Hello,

You have a problem in your program:

repeat
    intercom:=uart[1].rxcheck
    if(intercom > -1)
      uart[0].tx(intercom) 'Missing space, Tab

Duane Degn

I've had similar problems before. I think a pull-up resistor solved the problem for me. If a pull-up doesn't work, try a pull-down.

Duane

BTX

fbeek, is this usefull for you ?

repeat
    intercom:=uart[1].rx
    uart[0].tx(intercom)

fbeek

Hello,

thank you for your replies.

@Luis Digital: Thats a C&P Error.Sorry

@BTX: I will try it later but ich think thats not a nice way because the Programm hangs at this point. With rxcheck that can't happen.

Could it be that i must invert the tx signal?

BTX

I suppose if you invert the signal you'll get 0 instead 255, same problem inverted.
Use your code, don't worried to compare "if(intercom > -1 AND intercom < 255)", that sounds good for me, although talking about best programming technics, I'm not the best to answer you.

kwinn

fbeek, I beleive your problem is indentation. "uart[0]..." line will always be executed if not properly indented. 255 is decimal representation of -1. Try indenting the line.

mpark

What size is "intercom": byte, word, long?

fbeek

I found the problem. MPARK gave me the idea to look at the sizes.I changed it to long and now it works. Can you explain that for me? I thought the UART transmits byte/char values.

mpark

The rxcheck method returns -1 ($ffffffff) to signify no character. Storing -1 into a byte variable truncates it to the lowest 8 bits ($ff). Spin byte variables are unsigned, so byte-sized intercom ($ff) is not the same thing as -1. You could sign-extend it with ~ but then you would be unable to distinguish a valid byte of $ff from -1.

fbeek

Ahhhh....

Thank you now i understand the whole story.