Because of the Thanksgiving holiday in the U.S., TI E2E™ design support forum responses may be delayed from November 25 through December 2. Thank you for your patience.

  • State TI Thinks Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 3 answers
  • Subscribers 33 subscribers
  • Views 186 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

SN65C1406: RS232 transceivers

Ian Benton
Prodigy 210 points
Part Number: SN65C1406
Other Parts Discussed in Thread: TL145406, , SN75C1406, GD65232, MC1488, SN65C1168, SN75155

Have you lost interest in the SN65C1406, SN75C1406 and TL145406? I note that they are out of stock everywhere.

I have an application which needs an old-fashioned RS232 transceiver (2x TX 2x RX), because I happen to have +/-12V supplies, but no 5V supply and a 3.3V supply which can't support much current.

Your RS232 transceiver search

https://www.ti.com/interface/rs-232/products.html#286=2%3B3&287=2%3B3&sort=184nom;desc&

incorrectly shows the main supply voltage, so I can't search for devices with +/-12V supplies.

  • 0
    TI__Mastermind 46687 points

    Hi Ian,

    These parts are pretty much as uncommon as you can get in RS-232 devices for most modern applications. 

    a) 3T3R are not popular configurations (which all three devices you list are 3T3R - our configurations are mostly 1T1R, 2T2R, and 3T5R as are most RS-232 transceivers)

    b) It requires 3 separate supplies to function - where modern 232 devices only need 1 lower voltage source (mainly 3V to 5.5V) as they use a charge pump to generate high swing voltages. 

    We still do support the devices as they are still active and we do have stock in them, but it's definitely not a popular RS-232 device - most likely one of our least used devices in our offerings. Basically they are there to support legacy systems but if it's a new design we generally try to push for designers to look at the single supply devices - as it should be noted VCC is required and should be 5V even in the three parts you listed.

    1. They all have stock on TI.com -  not much but its there. 

    2. The main supply voltage is not incorrect in that table as the main supply refers to the VCC pin - which is 5V nominal for the three devices listed. Most modern devices operate off of 1 supply - not three - which is why it is setup the way it is.  You can kind of use VOUT column to determine which parts are not single supply - as it would be listed at 7.5V or greater - but  that's not a surefire way to check by itself - so if the device has VOUT >= 7.5V and the name doesn't start with MAX or TRS it most likely is a triple supply device that should be able to accept up to +/-15V - in your needed configurations that doesn't leave many options. 

    If you are concerned about stock the best alts. we have would be the GD65232 - it is 3T5R - which is overkill for what you need (more channels) but we have over a million units in stock it looks like at the moment - but it can work with +/-12V supplies. The other devices are there, but they are light on stock. At the moment they are still active.  Essentially the multi-supply RS-232 devices are largely legacy devices as modern RS-232 can achieve the same thing with less power and a much more streamlined design approach - I understand that may not be ideal for what you are looking for - but the parts you listed are active and the GD65232 may prove beneficial if the stock is an issue - but these types of devices (multi-supply) are not the focus of RS-232 development and haven't been for some time . 

    Best,

    Parker Dodson

  • 0 in reply to Parker Dodson
    Prodigy 210 points

    I only need 2T2R. I remember a whole load of devices that appeared in the 1990s from Motorola - MC145406 being one of them - they were 3T3R

    Is the 75155 going into retirement like the rest of them?

    Perhaps, as the baud rate is fairly slow, I'll use an op-amp, or build the innards of a MC1488/1489 out of transistors.

    I just need to get data in both directions between two boards in a large cabinet, and avoid the possibility of either end jamming the bus, so RS232 seems like a good, albeit boring, choice, as there is the possibility of some difference between the 0V levels.

  • 0 in reply to Ian Benton
    Guru 280040 points

    The large bus voltages of RS-232 are an attempt to increase the noise margin. But differential transceivers (RS-422, LVDS) are more robust regarding both noise and common-mode voltage offsets. See, for example, the SN65C1168(E).

  • 0 in reply to Ian Benton
    TI__Mastermind 46687 points

    Hi Ian,

    I understand you only need the 2x2 but for what your limitations with power supplies the smallest is 3x3  - they are still around due to legacy reasons as well. 

    For the SN75155 - it's still active -the SN75155D variant is not recommended for new designs - but the SN75155DR (same package as "D" variant but shipped in reel/tape)  and SN75155P are still active at the moment, so there is not official move to discontinue them yet. 

    I understand why approaching this application with a more hybrid/discrete makes sense - especially when working with older devices that we don't have a ton of alternates for. Your application is straightforward enough where I don't think you'd really see a lot of issues doing it discretely/hybrid versus a more integrated approach.  

    Please let me know if you have any other questions!

    Best,

    Parker Dodson