LTC2873 MODE pin question

Hi Sir,

We have question about LTC2837 .

The Mode pin can be dynamic configure with MCU ? have reference circuit ?

Thanks!

  • Hi Sir,

    We have another question,

    Connect DI to ground according to the reference circuit in the specification, May i know , why is it inconsistent with the table ?  can we using  DI / RO both ? 

    Thanks for your support. 

  • +1
    •  Analog Employees 
    on Nov 29, 2019 11:13 AM over 1 year ago

    Hi Elke,

    The 485/232 mode switch pin can be controlled dynamically. Refer to datasheet page 6 "Mode Change Characteristics" for timing specifications, and also the first diagram on page 9 for a plot of what would be expected viewing the mode change on an oscilloscope.

    Note that the 485/232 pin cannot be left floating - maybe consider a pull-up or pull-down on the board to set the default state in any case where the micro would not be driving the pin.

    DI is the driver input pin and is used for the data the micro is sending to the RS-485 bus or the RS-232 link. RO is correspondingly the receiver output back to the micro from the bus/link.

    The circuit copied below with DI tied low is a test circuit, not an application circuit, and is only for some test conditions that have DI in a DC state rather than clocking.

    Best regards,

    Conal Watterson

  • Hi Conal, 

    Thanks for help, In the datasheet page 16" function table "  for RS-485 TX/RX using right ? 

    In generally(RS-485) design circuit, DE485 and RE485 have to connect together.but the function table is shows  DE485 and RE485 different logic for TX/RX mode ? Compare the reference circuit in datasheet first page..  

    Thanks!  

    Regards, Elke

  • 0
    •  Analog Employees 
    on Dec 3, 2019 10:54 AM over 1 year ago in reply to Elke

    Hi Elke,

    DE and /RE can be connected together to simplify the control signals required, but they can be controlled individually if desired.

    The case you have highlighted is not so useful, as the receiver output is really only reflecting the transmission applied to DI and onto the bus from this node. A little bit like loopback except the true loopback (LB = 1) will not affect the bus.

    Regards,

    Conal