Hello,

this is old question but I had similar problem with reading input registers from address 0x3200 and far. I found very helpfull video from one programmer from Russia. There is writed Modbus RTU with RS485 communication SEND_PTP and RECEIVE_PTP function. It works perfektly.

https://youtu.be/EHKXNcAOIhw

Hello Nikoska and Smiffy,

Hope you all are doing well.

Can you believe that after more than a decade, the issue you discussed above still bothers me recently?

Yes, S1200,Modbus RTU, input register, data address of 0x7006, exceeds the range of 30001 to 39999. Until now, Siemens still has the limitation, which confused me a lot.

Fortunately, I found your discussion which is of expert and kind.

nikoska

Hello smiffy,

I understand what you are saying. But it's not that I need to access 65535 input register values simultaneously. Imagine that I need to access only 1 value, but which is not at input register address 1, but at address 53249. There is no way to do it with the S7-1200.

The fact is that a large manufacturer puts on the market ModBus Slave devices with this addressing scheme. Speaking to the equipment manufacturer (very large scale - thousands of these ModBus devices are in operation), they mentioned that several PLCs have this addressing limitation, but all of the ones they have encountered offer the capability to "offset" the input register address range by a user-specified value, so that you ask for address "1" and offset e.g. "0xD000", this is added internally to produce the final address of "0xD001" put on the bus. So, while you cannot access ALL 16-bit values simultaneously, you can access ANY of these values.

Of course, I could ask the manufacturer to reprogram their equipment to the 0-9998 input register address range, but even if they agree, this would only solve a single problem once. I would expect the most flexibility to exist in the controller and not in the controlled device. Thus my request for the addition of such an address "offset" feature in the S7-1200 firmware.

Thanks

Nikos