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Different TX and RX Baud Rates - How can this be?

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  • geometrix
    replied


    I removed the microOLED from another breadboarded circuit and replaced it with the new one that I am currently using. The microOLED works fine. This is a PIC24F or PICKit3 issue. Thank you.

    Leave a comment:


  • geometrix
    replied


    The splash screen comes up fine if I do not do the autobaud detect.

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  • ESPsupport
    replied


    What happens at different baud rates?



    Have you got a CE5 / MB5/ programming cable you can try connecting to the PC directly with?



    I tried a uOLED at 230kb and it worked as expected, so it's not some 'odd' baud rate.



    Since it's a 'one chip' display it's hard to see what could be burned out. There are a couple of protection resistors in the TX/RX lines, but if one of them was blown I wouldn't expect to see anything coming across.



    Are you getting the OLED spash screen up?

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  • geometrix
    replied


    Dear Moderator,



    The lines are "clean" before data is transmitted or received. Even when I step through the code using the debugger, I see the slow baud reply(ACK/NAK) to the fast baud transmit. Where could the noise be coming from?



    I have nothing on my benchtop that is creating that kind of noise.



    Is it possible that something is burned out on the microOLED? I have already swapped out the microcontroller.

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  • ESPsupport
    replied


    I suspect that, somehow, noise is being transmitted to the uOLED and that the autobaud mechanism is locking onto that noise.



    You should be able to see that by monitoring the lines and looking for the 242baud ACK that would appear to be sent before you send your 230kbaud 'U'



    Any ideas for the difference between transmit and receive baud rates. THEY SHOULD BE EXACTLY THE SAME ON THE SAME PORT.


    That's not quite true, for communication to work they will need to be within about 2% and hopefully less, but unless they are exactly the same device it is quite possible that they will be slightly different rates.

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  • geometrix
    started a topic Different TX and RX Baud Rates - How can this be?

    Different TX and RX Baud Rates - How can this be?

    All,

    I am using a 4D Systems microOLED-128-G1 display. I have used the device on other projects and it works well as a debug terminal.

    I am currently writing some new code for a new application using a Microchip PIC24F and I encountered an anomoly with the microOLED.

    On my oscilloscope, I noticed that the U2TX baud rate from the PIC24F to the microOLED seemed much faster than the U2RX baud rate from the microOLED to the PIC24F when communicating with the microOLED. In fact, I know that U2BRG on the PIC24Fis set to 250k using 4X PLL. I cut and pasted code from another application that I recently wrote, and that worked just fine with all of my UART configuration for U2.

    I basically send autobaud commands, clear screen commands, and formatted text commands to the microOLED. When sending the autobaud detect command to the microOLED (55h), I noticed a huge lag in the response of the microOLED as it transmits a ACK or NAK back to the PIC24F.

    So I used my logic analyzer to look more closely at the signal and this is what I discovered:
    1. U2TX is transmitting at about 230k.
    2. U2RX is receiving at about 242...not 242k, but 242.

    So the ACK/NAK is lagging so far behind that the transmits are essentially meaningless.

    Also, rather than receiving an ACK/NAK, it looks like the microOLED is sending back 55h and a NAK. The microcontroller should only be sending back a ACK or NAK...not a 55h. I have inspected the circuit to ensure that I have not shorted U2TX with U2RX.

    Any ideas for the difference between transmit and receive baud rates. THEY SHOULD BE EXACTLY THE SAME ON THE SAME PORT.

    TIA.
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