Hello all,

I have 1500 cpu with CM PtP RS422/485 HF. I tried to communicate using modbus master in TIA V13 but I got an error. The error I am getting is 0x81E2 (Check the settings for start bit, data bits, parity bit, data transmission rate, and stop bit(s).) . Im very sure about my settings, however when I looked here in the forum I saw some guys had the same problem in the past. which seems to be HW problem. I tried some of their solutions (for example to use resistor 120 ohm) but none of them worked for me.

That was at the client site, then I brought the sensor and the cpu+cp card to my office. here they worked just fine. so now I start to thing that something wrong with cable although I checked it several times and it was OK or something with the noise.

My question is, can the cable make this error? at the client site I use normal 4 wires untwisted cable (5m) long approx. 2 for power and 2 for the communication. while in my office I use simple untwisted 2 wires and they worked for me.

also, how I know that the site is noisy? and how can I avoid the noise? for example by using shielded cable or what.

T_Ebrahem

Hello T. Ebrahem;

Yes the cable and connections can cause this error.

See the documentation attached to this Application example, and the screenshot below:

https://support.industry.siemens.com/cs/ww/en/view/68202723

Hope this helps,

Daniel Chartier

dchartier

Hello T. Ebrahem;

Yes the cable and connections can cause this error.

hello dchartier

thank you for your quick answer, I saw this before but still I don't understand why, the cable was fine as I checked it several times and the connection was ok, even I reversed the A and the B just for check but I saw no difference. 

when should I start to worry about noise and interference?

the client is far away and I have to decide if I need to order a cable. so still not sure about the cause. 

also is there special cable for the modbus connection or I can use any shielded wire?

regards

T_Ebrahem

Kaulquappe

Hello T_Ebrahem,
do you get this error constantly or sporadically?

When you use parity even or odd and get this error constantly, you should change R(A) and R(B) at one side of your cable.

When you get the error sporadically you should check shield and terminating resistor.

Regards,
Kaulquappe

 hello Kaulquappe

I got it constantly and I changed the A/B and it did'nt solve the problem. also I tried the termination with 120 ohm which also didnt solve it.

I dont know what do you mean by shield here.

regards

T_Ebrahem

Hello T_Ebrahem;

Shielded cable has an overall metal braid or foil that surround the inner wires, to protect them from EMC and since it is grounded at some point in the network, also protects the signals from voltage spikes.

Shielded cable is used for analog signal transmission, or in serial networks such as Modbus or Profibus.

So you should check if the shield pof your Modbus cable is connected to the body of your RS-485 connector properly, so tit is well grounded (and eliminates some of the surrounding electrical noise).

Hope this helps,

Daniel Chartier

dchartier

Hello T_Ebrahem;

Shielded cable has an overall metal braid or foil that surround the inner wires, to protect them from EMC and since it is grounded at some point in the network, also protects the signals from voltage spikes.

Shielded cable is used for analog signal transmission, or in serial networks such as Modbus or Profibus.

So you should check if the shield pof your Modbus cable is connected to the body of your RS-485 connector properly, so tit is well grounded (and eliminates some of the surrounding electrical noise).

Hope this helps,

Daniel Chartier

 hello Daniel

I think the cable was shielded but not twisted, I will check it and I will order a new cable that recommended by the sensor manufacturer

thank you and I wish very nice weekend

regards

T_Ebrahem

Kaulquappe

 

T_Ebrahem

I got it constantly and I changed the A/B and it did'nt solve the problem. also I tried the termination with 120 ohm which also didnt solve it.

Then check again your parameterisation: baud rate, stop bits, paritiy, data bits. I expect it is a general / parameterisation error when you get the error constanty.

Regards,
Kaulquappe

 hello Kaulquappe

I believe that the parameterisation is correct as it worked in my office. mostly it is something with the cable.

of course, thank you and I wish very nice weekend as well

regards

T_Ebrahem

T_Ebrahem

 

Kaulquappe

 

T_Ebrahem

I got it constantly and I changed the A/B and it did'nt solve the problem. also I tried the termination with 120 ohm which also didnt solve it.

Then check again your parameterisation: baud rate, stop bits, paritiy, data bits. I expect it is a general / parameterisation error when you get the error constanty.

Regards,
Kaulquappe

 hello Kaulquappe

I believe that the parameterisation is correct as it worked in my office. mostly it is something with the cable.

of course, thank you and I wish very nice weekend as well

regards

T_Ebrahem

 Dear T_Ebrahem,

Atlast what did you do to solve this problem? Bcaz we are facing this issue now. And we are trying to communicate this for last 7 days. But nothing is worked out. The issue you were posted is replica of mine.

Regard's,

Haresh KM.