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Can a MLVDS half-duplex transceiver be created from a LVDS transmitter IC and a LVDS receiver IC?

Mike Valvo
Intellectual 470 points
Other Parts Discussed in Thread: SN65LVDM176, DS91D176, SN55LVDS31, SN55LVDS32

hello, let's say I wanted to create a 2-wire multipoint LVDS bus.  Rather than selecting a dedicated half-duplex device such as the SN65LVDM176 or DS91D176, where the transmitter and receiver are internally tied together, can I take a transmitter like the SN55LVDS31 and a receiver SN55LVDS32 and tie the input and output pairs together and produce the same results?  

  • 0
    TI__Guru 62910 points
    Hi Mike,

    Yes - it is OK to tie together the bus pins of a transmitter and receiver to create a half-duplex node as long as the driver has an "enable" control (so that it can be turned off when the node is receiving data).

    The two devices that you mentioned (LVDS31 and LVDS32) are designed to meet the LVDS standard (TIA/EIA-644), which is intended for point-to-point connections. You may want to instead look at some of our M-LVDS (Multipoint LVDS, i.e., TIA/EIA-899) devices. M-LVDS has some advantages over LVDS in these types of applications. It features higher output currents, which enable termination to be placed at both ends of the bus (important when any node can transmit or receive data). It also features slower rise/fall times so that the reflections from unterminated "stub" nodes have less of an impact on overall signal integrity.

    M-LVDS products can be found here:

    www.ti.com/.../multipoint-lvds-mlvds-blvds-lvdm-products.page

    Please let me know if you have any questions.

    Regards,
    Max
  • 0 in reply to Max Robertson
    Intellectual 470 points
    thanks Max. The reason I'm asking is because there doesn't appear to be any space-qualified M-LVDS products. out of the group of space products, the SN55LVDS31,32 are the only ones that mention multidrop in their datasheets, so I'm assuming that if I want to try half-duplex in space, then I'd want to use those chips. would you agree?
  • 0 in reply to Mike Valvo
    TI__Guru 62910 points
    Hi Mike,

    Yes, given the application it would make sense to go with the space-qualified LVDS31 and LVDS32 devices. Just be sure to take care with the bus topology, termination scheme, and stub lengths on the bus - if you are operating at high speeds then these can all have an impact on signal integrity. Let us know if there is any help we can provide.

    Best regards,
    Max