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RS485 wit AXI UARTLITE

Former Member

Hi,

I managed to use tty for rs232 via axi_uartlite and connected r232 pmod.

Now i wanted to use the rs485 PMOD via Linux on the Zedboard.

Therefore i wrote an IP-Core for setting DE / !RO.

My solution is to keep DE HIGH as long as the a LOW is written over TX. A Timer will keep DE High for at least WORD transmitted (let's say 10 Bytes) and will go LOW afterwards. Everytime a new LOW is written to TX the Counter will restart.

Via linux i can use the AXI-UARTLITE and send commands via tty but i cant receive them, only random ascii characters...

With a Scope i checked the DE signal and it works fine, but when i'm trying to read data it doenst work. But after a while it is possible to send data from pc to the pmod and read them via tty but then it's not possbile to send data via pmod... i hope you understood my problem.

Is there anything i have to think about?

I appreciate every help :)

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    Hello,

     

    It could be a lot of things. First, you might want to instrument both the DE and TX/RX signals to see the relationship.

     

    What protocol and transfer speed are you using?

    How long does the receiving unit on the other end expect the first 'low' to be?

    Does the delay from your IP detecting the low to asserting the DE signal truncate the signal too much?

    Does your timer that extends the DE signal assertion distort the signal received by the receiving node? ( would it make your Stop bit too long)

    How long does the other node wait before asserting a return message. Could the DE signal still be asserted and interfering with the data from the other end?

     

    Again, I would suggest instrumenting the data signals and comparing the results to your protocol and expected data.

     

    -Gary

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  • 0

    Hello,

     

    It could be a lot of things. First, you might want to instrument both the DE and TX/RX signals to see the relationship.

     

    What protocol and transfer speed are you using?

    How long does the receiving unit on the other end expect the first 'low' to be?

    Does the delay from your IP detecting the low to asserting the DE signal truncate the signal too much?

    Does your timer that extends the DE signal assertion distort the signal received by the receiving node? ( would it make your Stop bit too long)

    How long does the other node wait before asserting a return message. Could the DE signal still be asserted and interfering with the data from the other end?

     

    Again, I would suggest instrumenting the data signals and comparing the results to your protocol and expected data.

     

    -Gary

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