Hello,

I have a problem to understand how to organize the Register in the slave.

I don't know how to organize the HOLDING REGISTER in the Slave to work with BIT and WORD. Is it possible in the same register?

40001 means the begining of:

 - The REGISTER

 - Word Section in the Register

So how to work with BITs, as their range Address is 1-9999 and 10001-19999 ?

Begining of Register:

40001 WORD [0]

40002 WORD [1] 

40002 WORD [2]

...

40002 WORD [9999]

10001 BIT [0] ?

10002 BIT [1] ?

...

End of Register

Thank you in advance,

David

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Split from Please help Modbus RTU slave s7-1200 giving address.

Hello,

maybe question is, what device want that your bits (explain better what bits).

Hello Duris,

In fact I have a Master S7 1200 and 7 Slaves S1200 (slaves have the same data structure)

Slaves belong to another company, the network is farther than 200 meters and less than 1000 m, so we need to exchange data in Modbus RTU,

I have to :

Read bits (1 to 34)

Write bits (35 to 50)

Read words (1 to 20)

Write words (21 to 45)

=> I don't know how much registers I must use and what addresses I must use (offset 40001, 30001...?)

I just know that we have, in Modbus several tables:

Tables for bits:

- W/R     1 --> 9999

- R only   10001 --> 19999

Tables for Words:

- W/R     40001 --> 49999

- W/R     400001 --> 465534

- R only   30001 --> 39999

i know how to Read and Write Words in the area 40001-49999, I have created a Register Datablock in the slave (DB_REG = REG[0], REG[1], ..., REG[9998] : Corresponding to address 40001 to 49999)...

But how to make the program figure out that, now I need to work with bits? My Register Datablock is done.

Bits should be before this datablock, DB_REG=40001-49999.

How to work with bits now? Do I need to make a second call for FB_Modbus with DB_REG2=1-9999 ?

Thanks

Hello,

aaah so you're Master. I had feeling from your words that you're Slave. No problem, you can use simple sequencer, more Master blocks with different parameters depended to your requests with different recv/send areas. You can then run each needed block via some condition, as you need. Yes, look to Master block description, MODE value depended to Modbus Function Code and on the right side of description you see what values you need use.

Hello Duris,

Yes I'm Master, but I don't have yet the whole system to test. So I also need to make a sample program for the slaves (I have some s71200 for test in the office).

I don't know how to program those slaves.

Thanks,

David

Hello,

look to forum topics in Communication/Networks conference history. There are topics about SLave RTU configuration. You can also use PC as Slave with specific MB SW and connect via serial line with your PLC Master. Then you can check better your PLC code functionality.