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Original question:

MAX3243E: How to communicate between two auto-powerdown RS232 transceiver

MAX3243E: When does MAX3243E go into power off mode by auto-powerdown feature?

Kazuya Nakai59
Guru 21595 points
Part Number: MAX3243E
Other Parts Discussed in Thread: MAX3243

Hello guys,

One of my customers is evaluating MAX3243E which has auto-powerdown mode for their new products.

Their loop-back test (shorted RIN5(No.8 pin) to DOUT3(No.11)) was failed when the auto-powerdown mode is enabled (FORCEON=L, /FORCEOFF=H).

And the loop-back test was passed when the auto-powerdown mode is disabled with /FORCEOFF=L.

The related E2E thread

https://e2e.ti.com/support/interface-group/interface/f/interface-forum/1015120/max3243e-how-to-communicate-between-two-auto-powerdown-rs232-transceiver?tisearch=e2e-sitesearch&keymatch=MAX3243%20Loop

says that "With loopback, this problem cannot happen. TX_OUT will output a valid signal for at least 30 µs, which will keep the transceiver out of powerdown mode."

I think this mean is that MAX3243E doesn't go into the auto-powerdown mode as long as RIN is shorted to DOUT before MAX3243E is powered up.

Is my understood correct?

Also do you have any idea why did their loop-back test was failed when the auto-powerdown mode is enabled?

Your reply would be much appreciated.

Best regards,

Kazuya. 

  • 0
    TI__Guru 53575 points

    Hi Kazuya,

    Your understanding seems correct here. When a driver output and receiver input are tied together, auto powerdown should not occur as the loopback receiver will always have a valid input. One way this might not be the case is if the device was previously forced off (/FORCEOFF=L) which will put the drivers in a high-z state. The driver may remain in this state if the device moves to auto powerdown mode. To avoid this, /FORCEOFF should not remain high after power-up or FORCEON may be pulsed high to ensure the drivers become active. 

    Can you please confirm the state for the successful loop-back test? With /FORCEOFF=L, I would expect no data to pass through the device as the drivers and receivers (save 2B) are not active. 

    Regards,
    Eric Schott

  • 0 in reply to Eric Schott1
    Guru 21595 points

    Hi Eric,

    Thank you very much for your reply.
    Yes. the loop-back test was success except auto-powerdown mode.

    The customer connect /FORCEOFF to VCC and connect FORCEON to GND directly.
    As you say, once MAX3243 in power-down mode, the driver output will never be active
    because RIN voltage is always less than +/-2.7V in the test. So the test will fail.

    Is there any way to return the MAX3243 from power down mode to normal mode
    except FORCEON or /FORCEOFF controlling?

    Thank you very much again and best regards,

    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Guru 53575 points

    Hi Kazuya,

    The only other way to restore the transceiver to a normal mode would be to apply valid RS-232 voltage to one of the receiver inputs. Would it be possible to short the loopback receiver input or some other input to 5V for this test? This could be used to manually force normal mode with the mode control pins tied as you described. 

    Regards,
    Eric Schott

  • 0 in reply to Eric Schott1
    Guru 21595 points

    Hi Eric,

    Thank you very much for your reply.
    The reply is very helpful for the customer and me.

    Thank you again and best regards,

    Kazuya.