LTC2862A-2

Hi all,

I am trying to communicate with two LTC2862A-2 transceiver IC's. I set te first one on Transmit mode (DE '1') and (RE '1') and the other one on receive (DE '0') and (RE '0') hard coded in the two microcontrollers attached to it. If I send data to the transmitter the output lines are very nice the opposite direction when switching from '0' to '1'. If I look at the receiver side the receiver output pin "RO" is always high and will only drop 800mV with a zero. This drop is too little to be considered as a zero by the mircrocontroller. Attached some pictures, The pull up and down resistors are not placed, I set the DE and RE with the microcontroller. 

Thanks!

attachments.zip
  • 0
    •  Analog Employees 
    on Apr 9, 2018 6:32 PM

    Hi Rudy,

    To better understand and solve the problem, I hope you could provide more detailed information:

       1. What's the data rate and the length of cable you are using? Do you use the 10K Ohm termination resistor?

       2. When you start the communication between the two transceivers, do you keep the RE/DE pins at same stable logic state( both '0's or '1's)? If so, could you please probe the receiver side A and B bus signals?

       3. I see the "UC1_33_TX0" and "UC1_33_RX0" signals in your schematic, does "UC1_33_TX0" connect to the RX pin of the MCU? If possible, could you measure the RO pin of the transceiver when disconnecting the wire between MCU and transceiver?

    Regards,

    Neil

  • Hi Neil,

    Thanks for your fast response!

    I found the problem... I made a master/slave board in one and connected the master TX to slave RX then from the master TX to the transceiver TX to send the data to other slaves. This doesn't work because now is also the slave TX connected to the ''RO" from the transceiver.... I need an extra transceiver to accomplish what I want. 

    Thanks for your time. If you have a better idea that would be great. 

    Regards,

    Rudy

  • 0
    •  Analog Employees 
    on Apr 11, 2018 5:41 PM

    Hi Rudy,

    I would also recommend adding another transceiver between master RX and slave TX to avoid the collision.

    Regards,

    Neil

  • 0
    •  Analog Employees 
    on Apr 16, 2018 2:00 AM

    Hi Rudy,

    If you keep both transceivers in "Transceive" mode, then they would drive the bus at the same time, so the bus state is undetermined. You should set the other transceiver in "Receive" mode and you would see the received data from the transceiver's "RO" pin.

    Regards,

    Neil

  • Hi Neil,

    I changed the configurations and I tested the transceivers by setting one in transmit mode and the other on receive. This works great, but in the datasheet is written on page 8 that there is a mode that is called "Transceive", I would expect that if you select this mode that you can send and receive but this is not the case if I test it. I have set both transceivers on "transceive mode" and send with one the data. Nothing happens on the "RO" pin of the other device. In de datasheet is nothing written about this mode. Is there something that I miss? 

    Thanks and best regards,

    Rudy