SN65HVD3086E: SN65HVD3086E

Hi Krishnamoorthy,

How many nodes in the RS-422 bus - is the C8051F384 just talking with 1 other device? 

As for F/W development - RS-422 is protocol independent so there isn't a "standard" approach because the standard doesn't define firmware. RS-422 is usually referenced by higher level standards/protocols that would define this - so I don't think the keil IDE will have RS-422 specific library, but I may be wrong there - but it seems unlikely due to what the RS-422 spec defines. 

Generally speaking the firmware shouldn't be that different between Half and Full duplex - its the same control pins in either case: R is receiver output, D is transmitter input, DE is the transmitter enable (active high), and /RE is the receiver enable (active low). Since RS-422 only can have 1 driver on the line there shouldn't be any issue with bus contention and the receivers on the line (if always enabled) will be able to receive the message and send downstream for processing. How the system level application code process this information is variable depending on if you are trying to reach for a higher standard or not. If anything full duplex should simplify the overall solution and due to the nature of RS-422 all systems probably should be full duplex (unless the target of communication never needs to respond to the host).

If you have any other questions please let me know!

Best,

Parker Dodson

Hi Baskaran,

Yes you would most likely need a level translator to bring down the 5V logic to 3.3V logic (unless the MCU has 5V tolerant inputs which some do but a lot don't).

The VOH and VOL you can expect from this device are shown below:

So the typical high voltage output is ~4.6V (with a 10mA load current - many microcontrollers do not even request close to as much current so generally its closer to ~VCC - but either way the output impedance is very low)

So it would be advisable if the MCU does not have 5V tolerant pins to use a level translator - either something discrete or IC based as it should be a pretty simple implementation. 

Please let me know if you have any other questions!

Best,

Parker Dodson

Hi Baskaran,

Yes that should be an okay replacement - they should be able to perform the same applications without needing the level translator.

One thing to be aware of is that the data-rate max is higher for the 1476 which, even if you aren't maxing out the data-rate, will have a faster transition time which could create more high frequency content in the signal. In a point to point implementation of RS-422 I don't think this should be that much of a concern.

Please let me know if you have any other questions!

Best,

Parker Dodson

Hi Baskaran,

They are similar but there are a few differences (highlighted below are the ones that could negatively impact system depending on needs):

1. The fault protection range is slightly smaller for the SN65HVD34 - it still has some level but its a slightly smaller range.

2. It is not tested to the IEC ESD standard (the SN65HVD34). 

If these two things aren't that important in your application it should be okay - the other differences shouldn't matter (the 34 has higher input impedance - which will not negatively impact the application and the slower data rate is more in line with what is needed for your application so you aren't adding higher frequency content to the signal that you don't need to with a faster part)

Please let me know if you have any other questions!

Best,

Parker Dodson