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TRS3243E: Suggestion to resolve the detect issue when input 12V on DOUT pin

daniel
Genius 5095 points
Part Number: TRS3243E

Hi Team,

My customer use TRS3243E to connect a Cash Drawer device. The Cash Drawer side shorted pin1(DCD)/pin4(DTR)/pin6(DSR), so it would cause they are all 12V.

We found if 12V input to DOUT, the V+ voltage would be abnormal, and can not communicate with the Cash Drawer device.

Could you please give me some suggestion?

We have tried to add a series resister on DOUT, it seems work. But we are concern if this workaround would affect "Standard Serial Mode" behavior.

Power Serial Mode(Pin1 and Pin9 are power), Standard Serial Mode(Pin1 is DCD,Pin9 is RI).

Many Thanks

  • 0
    TI__Intellectual 1410 points

    Hi Daniel, 

    thanks for reaching out. I need your help to clarify some details.

    • My customer use TRS3243E to connect a Cash Drawer device. The Cash Drawer side shorted pin1(DCD)/pin4(DTR)/pin6(DSR), so it would cause they are all 12V.

    Q: Does this mean you have a fault scenario where the cash drawer shorts all pins together to the cash drawers 12 V rail or how does this happen?

    • We found if 12V input to DOUT, the V+ voltage would be abnormal, and can not communicate with the Cash Drawer device.

    Q: Yes the device pulls the communication DOUT signal up or down to the  V+ or V- of the charge pump usually the idle state is pulled up to V+ so the 12 V on DOUT while idle to V+ probably messes up the charge pump regulator and no communication is possible.

    • We have tried to add a series resister on DOUT, it seems work. But we are concern if this workaround would affect "Standard Serial Mode" behavior.

    A: Does this mean the 12 V are stll shorted to the DOUT? A series resistor is not too problematic until the value is not to high since the series resistor represents a voltage devider with th input resistance of the device.

     

    Kind regards 

    Dierk Bronner 

  • 0 in reply to Dierk Bronner
    Genius 5095 points

    Dear Dierk,

    Many thanks for the reply.

    The pin define of Cash Drawer as attached. I don't know if this is a regular pin define.

    Would you have some suggestion or workaround to avoid 12V input to DOUT?

    Thanks

  • 0 in reply to daniel
    TI__Intellectual 1410 points

    Hi Daniel,

    yes this is a RS232 standard pin out.

    probably whats going on here is that the customer tries to do is to is to simply the handshake by sorting together the pin1(DCD)/pin4(DTR)/pin6(DSR) -> handshake-loop.

    So if you now connect these pins to the TRS3234E it will see the 12 V of the other side. which probably messes up with the internal charge pump.

    I would suggest you to remove the connections on the schematic and do the same handshake-loop with the pins TRS3234E. It will providing its own 12 V by its internal charge pump.

    Can you try this solution and let me know if it is working

    Kind regards

    Dierk