Anybus 7808 Profibus (Master) Modbus RTU (Slave)


I am trying to test the module Profibus (Master) Modbus RTU (Slave). However, i have a problem with the Holding Registers.

I am using the program Modscan32 as a master to read and write data of a Siemens module in the profibus network. I can read correctly the information from the module, however when i try to write to the module, the holding register contains the same information than the input registers and it gives me an error if i try to force a bit or word.


  • Is this something that i may have configured or wired incorrectly in the Anybus module?
  • Could it be something wrong with the Modscan32 SW i am using for testing? Do you recommend? another program for this?

Note: I have been using the Modscan32 for the testing of a different anybus module (Profibus Master Modbus TCP/IP Slave and it works perfectly.


Marcelo Vega

Hello Marcelo,

I will review this issue to determine where the point of failure is.

Hi Kevin,

Thanks for taking this issue. How is it going? Any luck?



I haven’t been able to replicate this issue. I apologize for the delay, the Modscan 32 should work fine.
We usually use simply modbus.

What function code are you using? Are you writing to the Output buffer?


I used “simply modbus” with the same result. In modscan i used the code “03:Holding register” (40001-40030) to try to send commands through the Anybus module. I noticed that the “simply modbus” used a different code, but the result was the same. Both programs display the information of the input registers on the holding registers.

Marcelo Vega

Hi Kevin,

Tried again with both programs and the same issue. I try to change some configurations but the error still the same.
Is it possible that we can have a conference so i can show you my screen with the programs? This way you will be able to see it. I took some screenshots of the test. maybe you see what is the error.

Hello @Marcelo what modbus addressing mode are you using? If you are using modbus addressing mode you will read input registers and write to holding registers. If you disable modbus mode and use Anybus addressing mode you can use holding registers for all the data but will need to use a registers offset. take a look at the modbus register mapping in the Network guide.

Hi Deryck,
The addressing I was using is 30000 (30001-30030) for the input registers and 40000 (40001-40030) for the holding registers. I don’t have the option (or i don’t see it in the manual) you mentioned, however i found a table in the manual about the addressing and it worked. To read, i can use the range 30001-30030 for the input registers, but to write I must use the range 41025-41054 for the holding registers instead of 40001-40030. Thanks for pointing out addressing.

Thanks again

Glad to hear this helped. It looks like you are using Anybus addressing mode. The option is found in ACM.


Hi Deryck,

I dont have that option in my ACM. I see you have Modbus TCP/IP though this one is RTU. Not sure if I can do what you are proposing.

Please let me know

Ah, my apologies for some reason i was thinking this was a modbus TCP device. The modbus RTU device does not have this option. You were looking at the correct manual and mapping.


No problem.

Please, I have another question. I tested this unit with a RS232/RS485 at 9.6kbps, and it works well, however, if i try with 38.4kbps it doesn’t work. I connected directly to the ANYBUS module ( I changed the dip switch from RS485 to RS232 and the port baud rate settings of my laptop) and it also didn’t work. I am missing something? any ideas?


Can verify it’s RX to TX for the serial connection?

Also, what is the baud rate settings on the dipswitch?