When I change /RE High to Low,RXD OUT put became Low (about 260ns).
Could you tell me a reason?
The bus termination of 50 ohm is too low.
The RS-485 transceiver can drive a minimum 54 ohms.
For your specific question - can you please add a 1 nF capacitor between the A and B bus lines. Does the glitch on the RxD pin still occur?
Thank you for your advice!
I will try it !
If i try 1nF,It was settled,thank you.
I'm thinking the data rate to use in 100Ksps．
Is it all right to put the bigger capacity?
（Would you give me a advice max capacitor i can add between the A and B bus lines?）
Adding 1nF of capacitance is equivalent to adding a longer bus cable. 20 meters of added cable for example.
The 1 nF capacitance should not limit your data rate, especially as you are operating at 100 kbps low data rate.
I (my Customer）have one more question.
Why will RXD be LOW once 200 ns later after it's turned on?
I'm not making a corrugation indicate,the signal of A and B was checked separately, but transient overshoot and an under chute don't occur.
Is this the special quality of the device?
What is the cable length for this application? On short cables the capacitance presented to the bus pins is very small. With a very small capacitance the bus voltage will collapse to ~0V very quickly. This small capacitance will increase the possibility of RxD picking up false transitions on the A, B bus pins during power on/off. Adding the 1nF bus capacitance will increase stability and mimic the capacitance from a longer cable.
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