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    false receive interrupt when communicating with Max3232 with max232 using PIC

    Hello,

    i have two devices PIC18f4520 with max232 5v supply and PIC32MM0256GPM064 with max3232 3.3v supply both the device working correct individually i checked over modscan and modsim simulator, but when im connecting the PIC18f with PIC32mm via there max ics PIC18 received false interrupt when transmitting data i have checked it without even programing the pic32 pic18f receive false interrupt and it happen only when pic18f try to send data. Received data are some bytes are garbage and some are the transmitted ones.
    I doubted that while transmitting data from PIC18 on the other side means at pic32mm side max3232 drops the voltage level and due to that tout pin of the max3232 shift the voltage.

    Is anyone faced the same problem before?
    please let me know.

    Thanks
    Last edited by dhakeparag81; 20th June 2019 at 10:46. Reason: clarification

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    Re: false receive interrupt when communicating with Max3232 with max232 using PIC

    Sounds like some kind of MAX3232 connection or external wiring error. Give circuit details.



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    Re: false receive interrupt when communicating with Max3232 with max232 using PIC

    thanks FvM,
    i dont think its an connection issue i have checked it thrice already, also when transmitting data from pic18f it received correctly and sending data from pic32mm also received correctly in pic18f (missing first byte modnus protocol issue) but that issue due to receiving false interrupt on pic18f as i use it as master and it change the state of state variable due to that i missed that bye i guess will checked later.
    after observing on oscilloscope while pic18f(max232) sending data Dout pin of max 3232 on pic32 fluctuating that time pic32 was not program.
    and false receive interrupt trigger in pic18f only when pic18f transmitting.

    i dont have ckt diagram for pic18f side i have attached in pic32mm side im using RJ45 connector.



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    Re: false receive interrupt when communicating with Max3232 with max232 using PIC

    I don't understand the purpose of the various connections other than TX1, RX1 and GND in CN3. GND must be of course connected, otherwise false triggering can easily occur. It's also required that T1IN of the remote MAX2332 is pulled high to send idle level on T1OUT.

    You can short RX1 to ground and check if the unwanted reception continuous.



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    Re: false receive interrupt when communicating with Max3232 with max232 using PIC

    Hello FvM,

    Other connections are for SPI for Other board to interface which is currently unsued.
    Tx pin is pull up using 10kohm with vcc=3.3, also if GND not connected then that interrupt should be trigger always not only when the transmitting,and i have checked it its connected to the other cpu GND.
    The problem is when i interface MAX232 with MAx3232 and transmitting the data from MAX232 at that time DOUT pin of MAX3232 is fluctuate which is also equals to number of data send means if i sending 8 char then i get 8 time receive interrupt. Dout fluctuate means when there is no transmission then Dout is -3.3v approximate i forgot the voltage, but when transmitting from MAX232 it fluctuate to GND.



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    Re: false receive interrupt when communicating with Max3232 with max232 using PIC

    also if GND not connected then that interrupt should be trigger always not only when the transmitting,and i have checked it its connected to the other cpu GND.
    Don't jump in conclusions what should be, just check for complete wiring. I was asking about the ground connection on the RS232 side, between MAX232 and MAX2332. I see an open JP3 in your schematic, thus I doubt the connection may be missing.

    Dout fluctuate means when there is no transmission then Dout is -3.3v approximate i forgot the voltage, but when transmitting from MAX232 it fluctuate to GND.
    MAX2332 transmitter output voltage in idle state is below -5V, there's obviously something wrong in your circuit.



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    Re: false receive interrupt when communicating with Max3232 with max232 using PIC

    yes its connected

    - - - Updated - - -

    what will be the reasons to fluctuate DOUT pin while receving

    - - - Updated - - -

    previously we are using 1uf63v cap now change to 0.1uf63v all connections are same as diagram

    - - - Updated - - -

    just check the voltages at dout its -5, but after connecting it to the max232 its -3.5



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    Re: false receive interrupt when communicating with Max3232 with max232 using PIC

    just check the voltages at dout its -5, but after connecting it to the max232 its -3.5
    Must not happen. MAX232 input resistance is 5k and shouldn't load the MAX2332 so much. Either you have a connection error or a problem with the MAX2332, less likely defective MAX232. Check MAX2332 output with 5k resistor load.



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    Re: false receive interrupt when communicating with Max3232 with max232 using PIC

    Are you sure that the connection between the two MAX chips are correct. RX1 <- TX2 and TX1 -> RX2.
    If you are connecting the two TX's together the one with the lower voltage will dominate, due to output protection.

    I suppose you are using the RS232 sides on both drivers, not mixing logic and RS232 sides.



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