THVD1450: 485 BUS signal are occasionally synchronized --- THVD1450

Ken Zhang

Part Number: THVD1450

Tool/software:

A my account meets communication issue with THVD1450.

During RS485 bus communication, The signals on the A-line and B-line on the RS485 bus are occasionally synchronized and the waveforms are as pictured. What type of error may have occurred?

10 months ago

0 Clemens Ladisch 10 months ago

Guru 316440 points

This happens when one of the A/B connections at one of the drivers is broken. One of the bus lines is correctly driven high or low, but the other line is pulled to the same voltage through the termination resistors.

0 BOBBY 10 months ago

TI__Guru 72161 points

I agree with Clemen's analysis in terms of one of the drivers not being driven so the driver that is driving is pulling the opposite side through the termination resistor.

There's two possibilities I can think of on how this occured.

The first is what clemens stated with one of the drivers being broken though usually when a driver is broken it's shorted to GND or Vcc.

The second which I would guess is the reason why this occurred; one of the twisted paired cables is broken in a way that looks like an open circuit.

If the problem is the first one, then replacing the broken device would resolve the issue. You should know which device it is since it's the one driving the input pin D.

If the problem is the second one, then replacing all the cable would solve it. You could also check each pair for continuity to find which cable was causing the issue.

-Bobby