ST485BDR Spike occurence at A & B signal when controller Power ON and OFF

[xander0113]

Dear wonders of hardware enthusiastic,

I have an issue here. Whenever my board +5V on and off then on back, the (non isolated) ST485BDR A and B signals display spike and intermittent causing the RS485 software reader to hang. The type of connection from controller board ST485BDR to the RS485 software is via RS485 converter (non isolated type design).

Spike up to 9.8V. Description wise could be as unwanted signal noise generated during the ON and OFF cycle of the controller board.

Appreciate to have inputs and expertise on this matter.

Below is my schematic design.

[DrDiettrich]

@xander0113

Spike up to 9.8V.

Do you have long cables that introduce noticeable inductance?

[xander0113]

Its a short distance cable around 15cm (During testing phase).

[DrDiettrich]

What if you remove all earth connections?
To break ground loops...

[xander0113]

Tried that too. Condition still displays such anomaly at condition only A/B signal are connected.

[DrDiettrich]

You have so many components in your circuit. Standard modules will work with much less components. Why all those additions?

Remove all evitable components and add one by one until the spikes appear again.

[xander0113]

Point of view fair point. Noted on this here.. Appreciate the inputs