AB7641 Modbus Addressing


#1

We have a need to convert a Modbus TCP slave to a Modbus RTU slave, so I’m using an AB7641-F to accomplish this. What I want is to read the gateway with Modbus TCP and then have the gateway read the device at that same address (in the 40000-42100 range) with RTU. I noticed I couldn’t read at address that high and was wondering if I could shift the address range, but now I’m thinking I might have the wrong device. Am I actually after the AB7702?


#2

Hi @sbrc,

The addressing is static with the only option being to change the addressing mode between Anybus addressing mode and modbus addressing mode. See chapter 5 of theuser manual.

All of this being said if you have a modbus TCP slave then it sounds like you might have the wrong device. You would need to have a modbus TCP master to talk to your TCP slave then host the data as modbus RTU slave. For this you would want an AB9005.

The AB9005 still has its modbus RTU registers static, so you still will be remapping the data still. Unfortunately we do not have a transparent modbus TCP to RTU gateway only one that goes the other direction, modbus RTU to TCP.

Best regards,
Deryck


#4

Deryck,

Thanks for the response - I definitely have the wrong device. I think I explained this wrong, which is how we got here. I have a PLC that is a TCP master that needs to read/write to a VFD that is an RTU slave. The addressing needs to be transparent as I can’t change where the VFD addresses things. Do you have something that can do that?

–Shane


#5

Hi Shane,

We don’t really have a device that is a TCP master that can map data to specific modbus RTU registers. The best option would be the AB9005 which is a modbus TCP master to RTU slave. The mapping for the RTU side is staticly mapped to the memory of the communicator. You can map the RTU request to specific parts of memory but that I would recommend verifying the registers you need are accessible.

Regards,
Deryck