Hi,
Im am currently working on a project in which I need to interface my Siemens s7-1200 PlC to a SEL 751A relay via Modbus Rtu RS232 serial communication.
I wrote a simple program on TIA portal V12. Setting the PLC as the master but I am having trouble communicating with the Relay. For now I would like to make a simple test, read three values from the Relay IA,IB and IC.
First of all i am not sure if is even communicating at all. 
Second I am getting a status error for MB_COMM_LOAD and MB_MASTER blocks 
8180 Invalid port ID value (wrong port/hardware identifier for communication module)

I check the port id on the slave the SEL751a relay and it is 1. I am not sure what to do, I am new on to Modbus communication. Any help would be greatly appreciated. 

Note:
I was confused with the REQ for both COMM_LOAd and MB_MASTER, so I set a switched for both blocks, since REQ a positive edge I thought maybe opening and closing the switch would simulate a positive edge. 

Please Help anyone

Hello,

this looks like you don't have correct HW ID of communication card. Look to HW cfg of PLC and check on that communication module HW ID. That HW ID must be inserted to that communication instruction, this instruction must simply know which communication module is used.

Update: pls look, you don't specify your communication module used, this is very important info, how we can help you if you don't provide this info?

Ygor0191

Please Help anyone

My friend Duris told me the other day
that his cristall ball is in for repairs.

Could you help him out by attaching some
pictures of the coding you have done already?

(smile)

Hello,

hope this will be helpfull to you Ygor simply set correct HW module ID. You can also put correct HW address to Port via click on that Port, then you can have prepared that PORT as parameter, but you must correctly set value.

Update: but better help will be William's pictures with arrows (red/blue) showing exactly needed steps

Duris... I would recommend using the system constants.
I still think some screen captures from Ygor
will help you to zoom in to the issues more quickly.

For Ygor some steps:

(1)

(2)

(3)

(4)


When transplanting code from one project to the next,
the constant's name will should be the same
- but the number might change.

Note that the number I use now is different than what Duris uses..
which can be expected.

 Hi Duris_I

Im am using the CM 1241communication module. And I did check the hardware idenrifier which was 272. 

Thank you

Duris_I

Hello,

this looks like you don't have correct HW ID of communication card. Look to HW cfg of PLC and check on that communication module HW ID. That HW ID must be inserted to that communication instruction, this instruction must simply know which communication module is used.

Update: pls look, you don't specify your communication module used, this is very important info, how we can help you if you don't provide this info?

Ygor0191

 Hi Duris_I

Im am using the CM 1241communication module. And I did check the hardware idenrifier which was 272. 

Thank you

Has the suggestion from Duris help you resolve your problem?
If YES, please consider..
- Thanking Duris with an appropriate star rating.
- Mark the thread as closed.

If not yet resolved - feel welcome to continue the conversation.... and please add some pictures.

Regards.
w

William_B

Ygor0191

Please Help anyone

My friend Duris told me the other day
that his cristall ball is in for repairs.

Could you help him out by attaching some
pictures of the coding you have done already?

(smile)

 Hi 

Here are some screenshots of the code.

As i said before I want to read three current measurement from the Relay. According to SEL 751A Relay manual appendix E Table E.34 the User Map Register Values are in registers 126 to 250. Also according to S7-1200 manual Table 12- 69 Modbus functions, if I use MODE zero  I should be able to read the Read Holding registers 40001 to 49999. That is why in my code i made it so it reads the first 3 values on the Relay.

For The Master REQ I used a switch, to enable any time I want to read. But I keep getting a 8180 Invalid port ID value ERROR on the Master. 

Not sure if my Code is totally wrong or the Relay itself is not communicating.

Thanks 

More info:

Today I used ModScan64 to see in the Relay could communicate with My PC and it did. At first I was worry that my logic on the Relay was wrong. But given that it work with ModScan64 (I was able to Read and write to it). I am almost certain that something is wrong with my code. I am very new to PLC coding and please forgive me for my simple questions. Thank you again Duris_I and William_B for the support. 

I am not getting a 8180 Invalid port ID on the MB_COMMNDLOAD anymore. 

But my MASTER block is still given the 8180 error.

Do I need to add more to my code?