Hello Experts,

I would have some information about Modbus RTU communication when I need to access non standard memory area. It means I need to read and write registers out of Modbus range like 9900h for instance. (Mode:1, FC:06, Data_ADDR: 9900h (?))

S7-1200  has Modbus FB which working fine in case of standard registers. How can I handle registers out of range?

Thank you for your time.

BR

László

PS: Slave is an IAI PCON-CA linear actuator driver.

Jo nap,

in this case this value isn't still out of range, you can everytime convert value to DEC and see 39168. In this extend modbus range (higher than 9999) you need set higher value (extend range) -> 400001. I expect your required register (better check your original address) as 439169. Try that also +/- 1for sure. No problem to look in TIA help about MB blocks where is this range described and how to use this extend range addresses.

Hello, Duris_I,

THX for the hungarian greating!

Unfortunately I am failed with your suggession. MB_Master sends 8383 and 8188 messages with different settings on extended data_address. Maybe I am doing something wrong.

It needs more investigation... work is under progress...

BR

Hello Laci,

check in TIA help your STATUS values, they can point to some required investigation areas. Maybe one important hint can be set correct Slave address, it's value for Slave identification on network. Check TIA and compare value with yours. Also this recomemndation point also to real Slave defined address (you need check it on Slave cfg menu probably) and this address you need set in Master block. Don't hesitate ask next...

Update: maybe I recommend omit real Slave (of course check required settings) and use some PC MB RTU Slave simulation SW. You can easy set some required address of register and value, then you can from your PLC test communication. SW will return data or exceptions like real Slave. Of course it needs some real serial port on PC or USB to serial type adapter depended to your PLC serial module. What serial module you have on PLC, type (RS-232/485)?

Update2: Modbus RTU/TCP study here with Smiffy's topic or my favourite www.simplymodbus.ca

Hello Duris_I,

Thx for your activity.

Honestly I have worked with Modbus few times already. My experiance is there are numerous PLC manufacturer and type which can work any kind of Register_Addresses. (like omron, Keyence, and others).

Strange but I could send data to mentioned 9900h register of IAI roboCylinder drive with other PLC but Siemens. The reason why I need to solve this problem is that customer requrement of using S7-1200.

It means the register is really located on 9900h since I could read and write with different PLC.

Yes, I know simplemodbus and I have already bought they master and slave emulators few years ago. I made a homeautomation system with Raspberry Pi + PLC based on Modbus communication. Anyhow I can not be called expert of this issue.

I think TIA is as cube as it is and can not handle register addresses out of Modbus recommendation. Or can it??

BR

Hello,

no problem, also nice experience. Look to attachment where are some my defined TAG values that are for your solution. Of course I use Slave sim but this WRITE (FC6) - MODE 1 working prefectly. In DATA_PTR you need set some memory where is prefered <write> value for Slave to that register (I got there 45). Look to required register value as I already sugested, this is it 439169. I expect for first set correct comm settings depended to slave specification - speed, parity, ... Then is required execute for first MB_COMM_LOAD instruction (don't execute MASTER before you have clear DONE - true from COMM_LOAD). If you have DONE - true in COMM_LOAD, you can set that parameters to MASTER (MODE, ... or set already before) and execute REQ on MASTER. Check outputs DONE, ERROR. I think it must working, only required sequence need to be done.

 Hello.

PlcLaci

Hello Experts,

I would have some information about Modbus RTU communication when I need to access non standard memory area. It means I need to read and write registers out of Modbus range like 9900h for instance. (Mode:1, FC:06, Data_ADDR: 9900h (?))

S7-1200  has Modbus FB which working fine in case of standard registers. How can I handle registers out of range?

Thank you for your time.

BR

László

PS: Slave is an IAI PCON-CA linear actuator driver.

I have not had a need to go with Modbus RTU beyond the bare basics. My experience will not be helpful to you.

But I know of an FAQ that might be helpful ->
https://support.industry.siemens.com/cs/document/109474481

If this was not helpful and no other user can help you on this users' forum, please have a chat with Siemens directly. Contact Siemens' free support services through the "Support Request" button.

Your feedback is appreciated.

BR

UPDATE 1:
The Modbus RTU functionality has several versions. It would be most helpful to quote which functionality instructions and versions you are using.

#dP

UPDATE 1:

The Modbus RTU functionality has several versions. It would be most helpful to quote which functionality instructions and versions you are using.

Some additional notes:

There are differences between instructions starting with MB_* and those with Modbus_*. I recommend the use of the Modbus_* variant (but there is a catch - see picture).

Please see the picture for tips on this and more.

Hello all,

yes as #dP mentioned about some different instructions/blocks. I see this as HW depended, mean PLC firmware and also CM module or CB board used. Till this time I wait for some info from Laci  about his HW used. No problem to continue with conversations...