Hi All,

I am not able to communicate Modbus 5000+ Series of registers with one of the Slave device, details are as mentioned below.

1. CPU S7-1500, with CM PtP  [MASTER]

2. Socomec Countis E53 Power meter  [SLAVE]

Communication Parameters: RS-485 (RTU), BaudRate: 9600; Parity: None, Sop Bits: 1

I was able to read the modbus parameters in Modbus Software (Modbus Doctor), but i was not able to read the same parameters with Siemens 'MB_MASTER' block.

After going through the several threads in the forum, i tried changing the parameters in the MB_MASTER block, like changing the 'MODE' parameter to 0, 3, 103, 104 etc. And changing/adding  the value (3), (4) before the actual Modbus registers in 'DATA_ADDR'  parameter like 450520 etc, but still there is no success with that.

Can anybody please help/explain that how to access the 5000+ parameters with Modbus RS-485 with Siemens.

Regards,

Santosh

Would you please capture the Done / Error outputs and count how many times each one becomes true?  A couple of simple ADD blocks that adds 1 to a tag triggered from a NO MB_Master_DB-5_Done and another for MB_Master_DB-5_Error.

Then you can see if you are getting done or error.

If you are getting done bits, you are getting the data.

If you are getting the error bit, you want to save the STATUS output when the error bit is true and look up the error using F1-Help for the Modbus_Master block

The F1-help for the block is very extensive.  That said, it sometimes helps to know Siemens created a block where they try making the Modbus RTU requests slightly easier to understand - at least compared to older MB request blocks that use the "implied" leading 4 for reading registers.

Mode 0 is correct.

Have you configured the instance DB parameters (you have to click on the blue "Parameters" link in the F1-Help for them to appear)?

You have to "connect" - using to the MB_DB parameter of the instance DB - the Modbus_Comm_Load call to this Modbus_Master block.

What does your Modbus_Comm_Load call look like?  Or, did you not use it?

From F1-Help:

TIA Portal V15.1 F1-help - Modbus_Master: Communicate as Modbus master

Rules for communication by the Modbus-Master

• Modbus_Comm_Load must be run to configure a port so that the Modbus_Master instruction can communicate with this port.
• A port which is to be used as Modbus master must not be used by Modbus_Slave . You can use one or several instances of Modbus_Master¹⁾ with this port. But all versions of the Modbus_Master must use the same instance DB for the port.
• The Modbus instructions do not use communication alarm events to control the communication process. Your program must query the Modbus_Master instruction for completed commands (DONE, ERROR).
• We recommend to call all executions of Modbus_Master for a specific port from a program cycle OB. Modbus master instructions can only be executed in one program cycle or in one cyclical/time-controlled processing level. They may not be processed in different processing levels. The priority interruption of a Modbus master instruction by another Modbus master instruction in a processing level with higher priority results in improper operation. Modbus master instructions may mot be processed in startup, diagnostic or time error levels.

1) "Instance of Modbus master" here means a call of the Modbus_Master instruction with the same interconnection to a Modbus_Comm_Load instruction and the same setting for the MB_ADDR, MODE, DATA_ADDR and DATA_LEN parameters.

After reviewing the above copied rules, I think you will find your solution.

I will not assume you have the Modbus_Comm_Load block correctly configured and the instance DB (DB157) properly referencing the MB_DB.

Your posted image tells me you wish to request a read of registers 450520, 450521, 450522, 450523, and stuff that into "Modbus Registers"."500kW Data Read_Outgoing" which looks like a BOOL.

What I expected to see for DATA_PTR is an array of UINT or INT or WORD from 0..3 (length of 4).

Let's say DB "Modbus_Registers" has this starting at offset 180:

500kW_Data_Read_Register : Array[0..3] of WORD (or UINT or INT)

Then at DATA_PTR, this is all you need "Modbus_Registers".500kW_Data_Read_Register

Then you can access registers like this:

450520 as "Modbus_Registers".500kW_Data_Read_Register[0]
450521 as "Modbus_Registers".500kW_Data_Read_Register[1]
450522 as "Modbus_Registers".500kW_Data_Read_Register[2]
450523 as "Modbus_Registers".500kW_Data_Read_Register[3]

And if you want to read individual bits:

450520 bit 0 as "Modbus_Registers".500kW_Data_Read_Register[0].%X0
450521 bit 8 as "Modbus_Registers".500kW_Data_Read_Register[1].%X8
450522 bit 2 as "Modbus_Registers".500kW_Data_Read_Register[2].%X2
450523 bit 10 as "Modbus_Registers".500kW_Data_Read_Register[3].%X10

You can also insert UDTs in place of the arrays to transfer the data into the right location and give it a tag name that makes sense, like bit 0 = Running, bit 1 = Faulted, bit 2 = Ready, bit 3 = InvalidConfiguration, and so on.

Lastly, if you are able, I would recommend trying at least 57600 baud rate. If you are baud rate limited because of an existing Modbus RS485 network, that's fine.  Otherwise, 57600 should be possible unless you are not using proper shielded cable with the correct impedance for Modbus communications.  This guide can help: http://www.modbus.org/docs/Modbus_over_serial_line_V1.pdf

Most documentation states 9600 / 19200 are common baud rates.  If I cannot get 57600, I know I have a bad cable termination, poor cable routing, or the exact same brand and part # cable was not used throughout the Modbus network which messes with the cable to cable impedance matching.

If you are happy with 9600 and it works for you, that's fine. I am simply stating you may want to consider bumping it up until it starts to fail, then back it off at least one speed setting.

Santosh1989

Hi All,

I am not able to communicate Modbus 5000+ Series of registers with one of the Slave device, details are as mentioned below.

1. CPU S7-1500, with CM PtP  [MASTER]

2. Socomec Countis E53 Power meter  [SLAVE]

Communication Parameters: RS-485 (RTU), BaudRate: 9600; Parity: None, Sop Bits: 1

I was able to read the modbus parameters in Modbus Software (Modbus Doctor), but i was not able to read the same parameters with Siemens 'MB_MASTER' block.

After going through the several threads in the forum, i tried changing the parameters in the MB_MASTER block, like changing the 'MODE' parameter to 0, 3, 103, 104 etc. And changing/adding  the value (3), (4) before the actual Modbus registers in 'DATA_ADDR'  parameter like 450520 etc, but still there is no success with that.

Can anybody please help/explain that how to access the 5000+ parameters with Modbus RS-485 with Siemens.

Regards,

Santosh

Hi Huggy,

I have already configured 'Modbus_CommLoad' Instruction see attached PDF file, and its working fine for other 3rd Party Modbus Slave devices. 

Also i am using 'Done' & 'Error' bit from the 'MB_Master' block. Currently i have used 7-slave devices, out of that 1-Slave devices is not able to communicate (where the address register starts from 5000+ series) with Baudrate-9600. (See attached PDF for execution of 'MB_Master' block sequentially in the program)

The tag assigned for 'DATA_PTR' field in 'MB_Master' block is an 'Array of UDint'.

It will be difficult to use 57600-Baud rate because all other slave devices are in 9600-Baudrate.

As you informed i have added a counting tag for Done & Error Bits of the MB_Master block where i will be executing for reading the 5000+ series Modbus registers, only Error bit is incrementing not even a single time Done tag is incremented.

Regards,

Santosh

Hi All,

Sorry, for not mentioning the Counter part in my last attachment. Here is the counter logic which i have added for the 'MB_Master' Block Done & Error Bits with Status captured.

In the status when the Error bit is triggered, the block is giving the status as mentioned below.

16#81E2 - Frame aborted: Character frame error

Once again i have checked with Modbus Software to confirm the Communication parameters and wiring are correct to the slave devices, when i checked i can able to read the actual register parameters without any issue. Only thing i am doing in the Modbus Software is, i am swaping the words to get to see the actual values. (Data type of Modbus Registers is U32 for the Slave Device Id-8)

Communication Parameter Used are:  Baudrate: 9600 ; Parity: None  ; Stop Bits: 1  ; Data Bits: 8

So, can anyone help me how to proceed further please.

Regards,

Hi,

The new slave device is in the middle along with the other slave devices in the same line, haven't used any termination resistors on the end as the other slave devices doesn't required them. So by this i can say this device is not connected after termination.

Regards,

Santosh

Hi All,

Withe regarding the Communication issue which i was discussing in this thread, i was able to successfully establish the communication with the device which i am using.

Following are the changes made in the program, (Comms Parameter's are same as mentioned in my prvious replies) hope it may help others.

1. In 'MODBUS_COMM_LOAD' Block DB i have writing/forcing the few contsant data as follows:

a. ''Modbus_Comm_Load_DB''.Mode = 4  ;  b. ''Modbus_Comm_Load_DB''.Retries = 3  ; c. ''Modbus_Comm_Load_DB''.ICHAR_GAP = 0  ;  d. ''Modbus_Comm_Load_DB''.LINE_PRE = 2.

2. Added Termination Resistor (100ohm) on the both ends.

3. And the register to read the data from the meter (E53-Socomec) we need to mention the register with 50000+1 (i.e. Example: If the register '50514' gives the details of Phase to Phase Voltage: U12 then in our program we need to read it from '50515' with the Datatype 'UDint').

Apart from these all the configuration & programming blocks are same where we use for communicating with Modbus RS485.

Regards

Santosh