SN75HVD11: Rs485 communication line glitch

GEO FRANCIS

Part Number: SN75HVD11

Hi we are using SN75HVD11DR RS485 transceiver IC. we are configuring in full duplex mode. we are communication with two device distance of 1.5 meter.The cables are twisted pair.

when we transmitting the signal we are seeing some glitches on RS485 A-B line.

blue channel- RS485 Direction.

Pink Channel tx pin of the transciver

yellow channel RS485 A &B

Please find the waveform and schematic

over 6 years ago

0 GEO FRANCIS over 6 years ago

Prodigy 220 points

sorry, we are using in half duplex mode

0 Cristian Soltero52 over 6 years ago

TI__Prodigy 240 points

Hi GEO FRANCIS,

Since the device is going from receiving to driving the A and B lines could possibly be falling and rising at slightly different times during this, which might give that slight glitch right when the driver is enabled. Can you probe the A and B lines separately on the scope? Also, is this negatively affecting your receiver output?

Best regards,
Cristian Soltero

0 GEO FRANCIS over 6 years ago in reply to Cristian Soltero52

Prodigy 220 points

Hi ,

I was in vaction. we have probed the signal. please find the attached image.

0 Cristian Soltero52 over 6 years ago in reply to GEO FRANCIS

TI__Prodigy 240 points

GEO FRANCIS,

I just ordered the parts to review this problem, and I will get back to you soon as possible.

Regards,
Cristian Soltero

0 Cristian Soltero52 over 6 years ago in reply to Cristian Soltero52

TI__Prodigy 240 points

Hi GEO FRANCIS,

In looking at the parts, I did not find any inherent glitch on the bus when the directional signal goes from LOW to HIGH. For RS-485 communication there is usually a time in between transmitting data where both drivers are off before pulling one driver HIGH in order to avoid any overlap as two talking RS-485 transceivers should not be active simultaneously. What is your duration of this time?

Best Regards,
Cristian Soltero

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SN75HVD11: Rs485 communication line glitch