Linux/SN65HVD73: communicate SN65HVD73 and SN75C1168

Hi Yukihiro,

You should be able to use these parts together in your system.  Would you mind sending a network diagram to us just so we can clarify any potential problems that could arise in the system-level design?  Is there a specific reason that you are not using SN65HVD73 on both ends?

You may want to keep a few things in mind when using these two devices together.  

I noticed that the Receiver input threshold ranges on the SN65C1167 are +/- 200mV.  This may cause an issue if at any time the A/B pins are shorted together in a fault condition.  In this case, the receiver input differential is 0V, and will be in an indeterminate state.  The R pin may output a high or a low, depending on the previous state of the bus before the fault occurred.  To prevent this indeterminate state, many transceivers are designed with input thresholds offset from 0V, like the SN65HVD73 (-200mV to -20mV).  These thresholds are still in the spec of the RS-422 standard, but they allow a determined (High) output on the R pin in the case of a bus fault.

The SN65HVD73 operates up to 20Mbps, but it's receiver propagation delay is significantly longer than the SN65C1167 device (40ns maximum versus 27ns maximum).  What operating speed are you planning to run on your system?  

The SN65HVD73 functionally operates across -7V to +12V common mode voltage on the bus.  The SN65C1167 only operates with +/- 7V common mode.  This may affect the grounding design for your system.

Do you plan to operate your system above 85C temperature?  The SN65C1167 only functions from -40C to 85C.

The SN65C1167 has a higher driver output variability than the SN65HVD73.  [Specs like VOD(del) and VOC(del).]  This device may have higher electromagnetic coupling onto your system.

In place of the SN65HVD73, you may wish to consider our new THVD15XX family of devices as well.   They offer improved performance in areas such as higher ESD protection, improved common mode voltage range (+/-15V), and lower quiescent current in similar package sizes.

Best Regards,
Max Megee

Hi Max Megee.
Thank you for your answer.
I attached parts of our circuit diagram.
The reason why we don't use SN65HVD73 on both ends is SN75C1168 board is already fixed and used in our machine.
Though we don't care about shortage between A and B, we watch out for line open.
Regarding line open, both of our circuits has I think no problem.

Our machine's operating speed is 10.5Mbps and we use it within 85C.
In the datasheet of SN65HVD73, receiver propagation delay is written as 90ns(max).
Does this mean we can't use this device for a speed of 10.5Mbps even though SN65HVD73's speed definnitoin is 20Mbps?

This time we need to use RS-422 device with 3.3V supply voltage in some reason.
That's why I am considering to use SN65HVD73.

Best Regards,
yukihiro

Yukihiro,

Thank you for the details. I think you should be just fine to use these two parts together. You should not have a problem operating the SN65HVD63 at 10.5Mbps. I see that you have already implemented a fail-safe resistor network with R319 and R320.

Please let me know if you have any further questions.

Best Regards,
Max

Thank you Max.
I want to confirm about receiver propagation delay "max 90ns" of SN65HVD73.
If operating speed is 12Mbps ( period is 83ns), does it mean I can't use SN65HVD73?
Best regards,
Yukihiro