Hi guys and gals.

I have an ET 200SP with a CM PtP (6ES7 137-6AA00-0BA0) that I need to communicate with over Modbus with several third-party modules. I have has success with a device that is 8 data bits, Even parity, 1 stop bit. But now I am tying on a device that is 8 data bits, 1 start bit, 2 stop bita No parity and ant getting nowhere.

For the first mentioned device I set the PtP config 8E1 and 19200 in the Modbus_Comm_Load_DB I have changed the Mode to 4 (half duplex), no problem, I can both read and wright from the device. This devise does not say anything about start bits and I cannot find anything in the PtP config nor in the Modbus_Comm_Load_DB where you could change that.

For the second device I do the same changes to the PtP config, 8N2and 19200 and in the M_C_L_DB I also set the stop bit to 2. The error I am getting is 0x81E2 (Check the settings for start bit, data bits, parity bit, data transmission rate, and stop bit(s).)

I have fore types of devices that I need to read from and only one of them mentions that it has 1 start bit. That specific device is the only one that only allows me to configure the baud rate and ID. So I figured to change the other three to the same parameter as that one (8N2, 19200).

Can you tell me where I see and change the amount of start bits? And perhaps lead me to what I am doing wrong?

Regard HannAri

Dear smiffy

Thank you for your help but I haven’t solved the issue yet. Now I have gone back to basics were I only have one Maser block and one slave device connected to the PLC with a good quality screened cable. I set the Port parameters (se attachment 1) and the stop bits in the Comm_L block (see att. 2). I set the baud rate to 19200, parity to 0 and response time to 1000 (I have tried 3000) (se att. 3). I make the Comm_L.Done set a bit that triggers the request on a function I made that contains the master block (see att. 4 and 5). The problem I am having is that I get always around 10-50 errors (81E2) and then the master.done goes high and stays that way and the master.error stays low (see att 5). Every time I stop and rerun the CPU the same thing happens.

If I then change this same devise to 8E1 and set the PLC accordingly everything works.

Can you tell what the problem is?  

Best regards,

Ari

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I'm a little confused about what you're trying to accomplish.   The way I read it, 8-E-1 works, 8-N-2 does not work.  So use 8-E-1o.  Forget about 2 stop bits.
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Hi Dan.

My problem is that I will have to connect to several devices that only have the option of being 8N2. Now I am just using another devise that has the option to change between 8E1 and 8N2. As I stated before then I have no problem connecting to it when it is set to 8E1 and the PLC correspondingly but as soon as I set the devise and PLC to 8N2 then I get error 81E2. I have a software that comes with that specific device that can read from it fine also I use a third-party software that can as well read from it whether it is 8E1 or 8N2.

So what you are saying is that the Siemens PLC’s do not support no parity and 2 stop bits?

Regards Ari