Access coils/bools

Hello.

short question. After long search and reading all discusses on this topic I get that point. 

It´s not possible to read/write a single coil/boolean in a holding register. It´s possible to read/write the whole word and get the binary value through splitting the word in its 32 bits. An oder possibility to access coils/bools is by transfering them into the input/output words and than access them with the fc-codes  01, 02, 05, 15. So to acces the output bit Q70.1 we need to: 70byte * 8 Bits = 560 + 1 = 561.

Thats the only way I found to get directly on the bools. Am I right? Can someone pls confirm proof me wrong?

Thank u all.

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Split from read/ write coils or discrete inputs through Modbus tcp.

Hello,

An oder possibility to access coils/bools is by transfering them into the input/output words and than access them with the fc-codes  01, 02, 05, 15. So to acces the output bit Q70.1 we need to: 70byte * 8 Bits = 560 + 1 = 561.

yes but be careful how you do that interpretation of addressing - Input/Output Words. Really from this description is not clear where you want to do that. Access with FC1 and next depended to Coils and Inputs are not possible to address to HR with this access option so only to PI/PO areas. This is important to say. Also you need differ between FC1 and FC4 for sure. Next important idea is if your CPU has only lets say Q0.0 to Q0.5 (typical S7-1200) available outputs, what is then available as count of coils? Try also test this, this is very important test to know finally how it is working also with this situation.

Hello,

thank u for ur quick response

Access with FC1 and next depended to Coils and Inputs are not possible to address to HR with this access option so only to PI/PO areas.

Yes that´s the point I get to. So I guess it´s not possible either to access Coils in HR with other FC-Codes (2, 5, 15)

This is important to say. Also you need differ between FC1 and FC4 for sure.

Yes thats clear too. Because 1 is for coils and 4 for hr.

Next important idea is if your CPU has only lets say Q0.0 to Q0.5 (typical S7-1200) available outputs, what is then available as count of coils?

In this point my description is maybe a bit inaccurate. I don´t mean hardware I/O but the complete address area. So for my Hardware i use q0.0 - 1.1 and for receiveing date via modbus I use in the Output words q70.0 . . .+.

Via Modbus I want to control my S7-1200 (MB_Server) with IO-Broker (Client).

For this I need to send and get Reals, Integers. And Bools. Real and Integer are working fine. (I used an DB with Arrays for this)

But I as we know we can´t acces coils in a hr.

So what do you think? Should I store all Data in I/O Area or does it make more sense to store Reals and Ints in DB and just the bools in I/O Area?

Thanks a lot

Hello,

Yes thats clear too. Because 1 is for coils and 4 for hr.

FC3 for HR ok no problem. It's up to you what strategy you select. As inside one of other Topics, idea of using bool access via HR is also possible but I recommend everytime to use standard options. If your situation needs to do that workarounds then good description inside your documentation is required, although standard interface of data access is broken. Other 'users' maybe expect standard access tests with your Server what will be not possible because instead of your Coils access inside PO areas, you'll have them mapped inside HR. Typical example.

You're welcome!

Glad you did your tests and hard work to understand all. No better experience than own and with tests. Good luck.