Hi,

yes, sorry for the delay, I was expecting email, forum did not notify me about the PM.
Anyway, as I recall I had same problems with hardware vs software and I used other blocks for MB RTU communication.

Please use the other ones:

S7 Smuck

Hi Vulpes,

have you had a chance to look at the code?

Cheers.

Oh - ok. Are they in the libary?

Not infront of my PC today!

The comm load is happy with a 0000 status, as is the Modbus slave also 0000 status.  My gut feeling is the mode 4 setpoint in the CM 1241 but on the older style blocks you cannot set this in the DB?

Is there a way to confirm the CM1241 is in mode 4?  There are no DB for the hardware.

The Modbus scanner is no picking up anything other than 000 as a reply.  I did upgrade the CM1241 to version 2.1.  I hope this isn't the reason!  I have tried another CM1241 and its the same result.

Any ideas?

1. cable? Pinout is ok?

2. FW version of the device and CPU is OK in the project?

3. I saw in You'r poroject You had master and slave called in OB1.Try only one. Slave in this case. Use some simple new DB (remember block access) with a straight-forward data.

4. How do LEDs on CM behave? Both blink, one blinks?

Not sure what You mean by "mode 4 setpoint in the CM 1241"....?

Hi S7_Smuck,

Please post your MB_COMM_LOAD and MB_MASTER (or MB_SLAVE) rings to see where the problem.

Data!!!!!!!!!!!!!!!!!!!!

After checking everything I could, I did a factory reset, re-compile and download.

The Modbus scanner jumped into life en voila !!!!!!!!!

Can't believe how long it has taken but were there now - finally.

Thank you all for the assistance - Especially Vulpes for enduring my stupidity.

Siemens - really.  Having to use an older working version of the Modbus slave and comm load functions is farcical.

If new function blocks are added , the documentation should also reflect the new functions. - with working examples!

I don't doubt the new blocks work, but despite many attempts I couldn't get it right.  It really shouldn't be that hard.

Thanks again to the forum mob. I salute you!

Hello

For modbus RTU 485 network using DB-9 pin connection will be

3--> A

8--> B

5--> GND

now regarding programming you need to configure MB_Comm_Load block with first scan bit, parameterize block properly using its help, your configured block is correct.

now for using MB_Slave you need to understand few things 

MB_ADDR--> modbus slave number your are defining this number for plc as a slave & should be unique.

MB_Hold_Reg--> you need to give pointer address here, you can create DB & add required length of the data to be send. starting address of the pointer will represent modbus holding register address- i.e.40001.

if you are using DB3 for modbus slave data area & you are sending suppose 10 words i.e 10 holding registers then 

pointer :- P#DB3.DBX0.0 byte 20

--> DB3.DBW0---> 40001

--> DB3.DBW2-->  40002

& -------

--> DB3.DBW18--> 40010

Likewise.

you can use DBW address also if you are sending single word data.

just check your DB optimize access setting once to use pointer address.

also in MB_Comm_load  once add one unused bit in parallel at Req parameter & force that bit & check if there is any error is reflecting or not & correct the same if it is.