Hi all,

my system uses ET 200SP as decentral peripherie and S7-400H as the CPU. I have ET 200SP PtP CM (6ES7 137-6AA00-0BA0) installed, to be used as Modbus slave interface (RS485 2W).

As far as I understand from the (very confusing) online documentation, I have to use, in my user program, the following blocks:

FB611 (Send_Config) V1.0
FB612 (Receive_Config) V1.0 / UDT580 (Receive_Conditions) V1.0
FB613 (Send_P2P) V1.2
FB614 (Receive_P2P) V1.1

FB640 (Modbus_Comm_Load) V1.0
FB642 (Modbus_Slave) V1.1

that can be downloaded from Here. So I have placed them in my block folder (remember, I must use Step 7 V5.5 since I am on S7-400H) but now I have several questions:

1. When should the FB640 called? I guess only once, or upon request if communication parameters must be changed during runtime (eg. from an HMI), setting the REQ input to 1, then reset it to 0

2. How to assign the PORT parameter to FB640? E.g my CM has address 572 in HW configuration, shall I enter W#16#23C?

3. How to assign the BAUD parameter to FB640? The documentation shows a code (6 for 9600bps, 7 for 19200 and so on) while someone in this forum says it has to be explicit like L#19200). Please shed some light on this topic

4. While compiling my blocks, I get an error on FB642 "Modbus Slave", requiring UDT 612. Where can I find this UDT?

I am attaching a printout of my OB1 and OB100 so that you can comment and suggest improvements

Hello,

Have look in attached project backup. I haven't test full functionality of H with Modbus RTU but test it and let us know the result.

Thank you for your help,

looking at your example, I probably guessed right on how to configure the communication. I will try and let you know.

Stefano

Hi all, everything worked fine except:

- if I remove and reinsert the module, or if I power cycle the ET 200SP chassis, the communication does not restart automatically. The only way I have found to make it restart is to STOP/RUN the CPU.

- if i set the initialization parameter of the modbus slave FB, the communication stops and I have to STOP/RUN the CPU

any hint? Thank you.

Edit: attached S7 project (communication part only)

Hello,

have not looked to your project but in my opinion one problem can be with initialization of communication - Modbus_Comm_Load. I expect this block located in OB100 initialization or with first scan bit set, so therefore this can be problem. If you'll prepare needed checks and asociate this paralelly with input condition of Comm_Load, you then can initialize your communication also without init of your system. Only idea, all business I leave for your implementation.

Dear Duris_I,

Modbus_Comm_Load is recalled within OB1. Initialization parameters are set in OB100 and everything woks properly. if I try to set the same parameters online, when the system is already running, I have no effect

Hello,

basic question only, you've mentioned that you need restart CPU, which CPU (S7-400/ET200SP)? S7-400 does light some diagnostic LED in case of reinsert module? what about diagnostic buffers on both CPUs?

@DJ_1Thank you very much. It worked like charm.

This is what I did,

"Copied all the blocks available in the Library program that I have downloaded for CM ptp module (Modbus RTU V1.3)  to my Newly created program. Then configured the port(PI Address of CM card), mode , line_pre, baud for Modbus_com_load. Then defined slave addr, data addr, data length, data_ptr. And it worked well. 

If your configuration is ok then you will see the CM cards TX is on(or blinks) even without a slave device.

If you see Area length access error for FB641 or FB640, this is due to blocks/udts are missing. Modbus RTU communication will not work if you have those error."

Thank you again.

Hi friend,

Can you please share the working backup.

Thanks,

Zakir Sayed