ADM3252E - RS232 output Issue

Dear Analog Devices,

I use ADM3252E as a level shifter (converting TTL to RS232 and vice versa) in a project. Data is generated by a microprocessor at TTL the voltage level, and then pass through ADM3252E so that a communication is provided between the PC and microprocessor. When the RS232 connector is not connected to the PC, the data is clear and has a voltage rating of (-8V to -5V & 5V to 8V) and there is not problem. However, when the RS232 connector is connected to the COM port of the PC, the voltage level decreases dramatically. The voltage level is between -1V to 1V, so the voltage rating is not provided for RS232 standards. Therefore, the data is transmitted to the COM port of the PC. How can this problem be solved? Why does the voltage level decrease?

Note: The charge pump capacitors are selected to be 220nF, but 100nF and 2.2uF capacitors are also used and no change was observed. 

  • 0
    •  Analog Employees 
    on Jan 13, 2020 1:33 PM over 1 year ago

    Hello Ryaman,

    Can you please confirm the model of cable and details of the PC you are using? Does the PC have a native serial port (DB9 connector) and is it correctly configured, or are you using USB to RS-232?

    It seems likely the ADM3252E is working correctly if the correct voltage levels are present on the connector. Can you attempt to connect to a different RS-232 node (e.g. evaluation board or Arduino board) with another cable?

    If the cable model isn't known, you could verify that the pin connections at both ends are as expected (not crossover or broken) to make sure there's no miswire issue.



  • Hello Conal,

    We have made some observation and changed some parameters regarding the software of the ATMEL. The data is now transmitted when we use a RS232-to-USB converter. However, this is valid for UART0 of the ATMEL. UART1 of the ATMEL does not work. Therefore, we could not find the root cause of the problem.

    Best regards,

    Ramazan Yaman