Illegal modbus response from serial card

[azwhoony]

Hi,

I can't view your vi. I'm using LV 8.2. Can you resend with 8.2 version.

Thanks 

Azni

[K C]

Hi Azni,

Sorry, here it is.

[azwhoony]

Hi KC,

I don't think the module support the loopback function. Please see attachment. Any other way? Really confusing...hmm..

Thanks.

 Regards,

Azni

[K C]

Hi Azni,

The error you get (-1073807253) is a framing error. This has nothing to do with the MB protocol.

This means that one of your basic COM settings is wrong or your communication link is bad.

Did you get this error before you tried the loopback test ?

[azwhoony]

Hi KC,

Yes. I also get this error even before the loopback function. All settings for the port and equipment are the same so I don't think that this is the one. I already checked with PCI card supplier and they said everything is correct just the way I did. They already tried the same environment on their side and it seems ok. This bad linkage that you mean is it physical connection? I swapped the 2 RS485 wires also doesn't work.

If I used on-board com port, if i swap the wire and it is the wrong connection it shows Timeout.

If I used PCI port and it is the wrong connection, the recieve string became even worse. If the connection is correct most of the time it will shows the error but sometimes I get the valid response. Just like the jpg image that I posted before.

The framing error could it be something to do with the microcontroller program inside the hardware itself or grounding issue?

Thanks.

Regards,

Azni

[K C]

Hi Azni, Before you said the transmission was sometimes OK. So it must be the hardware link. Do you use a active and passive terminator at the ends of the RS--485 cable ? With a short cable and one device the passive termination is not important (but should be connected) but the active one is important. The ground reference of all connection should be within the common mode range of the RS-485 tranceivers. Can you tell me how your physical link looks like ?

[azwhoony]

Hi KC,

I don't quite follow you? Termination at the end of 485 line? How should I do that?

Thanks.

 Azni

[K C]

Terminators is a standard RS-485 item.

On onside (the master) there must be a active terminator on the other side the must be a passive terminator. With side I mean the begin and the end of the cable.

Terminators are resistors. A active terminator puts the RS-485 signals in between the VCC and ground level. The passive terminator is a resistor (typical 120 ohm) to terminate the transmission line correctly.

Most devices already have those terminators inside but you have to connect them through outside connections or switches. Check your datasheets/manuals for this.

[azwhoony]

Hi KC,

There's been some mistakes in the jpg file before. Please see the new one. If you mean by 120ohm resistance, we already tried that and the result was the same. So we took out the resistance already. About the active termination at the other side, can you explain a little bit more how should I do this? This one should be at the PCI card?

Thanks.

Azni

[azwhoony]

By the way, I already checked on the manual and the termination part is not stated anywhere.