SN65HVD75: SN65HVD75DR

What signal did you measure? What other resistors are there on the bus?

KM,

The TX is an input signal from a controller, so not necessarily affected by the transceiver, and your schematic doesn't indicate any reason that the input signal would be attenuated. As Clemens asked, what signal is being measured and where on the schematic?

Regards,

Eric Hackett

Hi All,

Thanks for your reply, please refer to attached waveform for more detail.

We measure the RX/TX from MCU for reference, and Ch-1 measure the A/B signal, Ch-2 measure the RS485 direction control pin.

We are wondering why the A/B voltage signal seems abnormal (0V ~ 3V only instead of -3V ~ 3V) when MCU transfer data via SN65VHD75?

Thanks.

How are you using a single channel for measuring A−B? Is this a differential probe?

The measurement shows that at least one output pin is not driven in the low state, i.e., that the transceiver is damaged. Do you have the same problem when you replace the chip?

Hi Clemens Ladisch,

How are you using a single channel for measuring A−B? Is this a differential probe?

KM: We use one single probe to measure A-B signal, B connect to ground and A connect to the other side.

The measurement shows that at least one output pin is not driven in the low state, i.e., that the transceiver is damaged.

KM: We have tested at least 3 pcs board with same issue. So based on your experience, this symptom shall be related to IC damaged right?

Do you have the same problem when you replace the chip?

KM: Not yet, will try.

Thanks.

KM

Hi Clemens Ladisch,

Thanks for the reminding, we will check the waveform again with your method.

Regards.

KM

Hi all

Based on your measurement suggestion, here's what I've measured before.

It seems this SN65HVD75 still cannot transmit TX signal to A-B bus.

Now our MCU can get RX signal from SN65HVD75, but SN65HVD75 can't transfer TX properly.

Any comments about this?

Thanks.

Jerry

Please tell us how you have connected the C1/C2 probes.

Hi Clemens Ladisch,

Please see below figure for Probe C1 & C2 connection.

Thanks.

KM

Hi Clemens Ladisch,

About how to connect C1/C2 probe, please refer to KM's reply.

Do you have any comments for that?

Thanks.

Jerry

Assuming that all the grounds are the same, the device appears to be damaged.

You said that you tested three boards with this issue. Are there other boards that work? If yes, then the most likely cause would be overvoltage (ESD, electrical noise, etc.).