Hello,

Sorry but half information can get only half solution.

Which PLC version? Which software version? Is it MB Master or MB slave?

Who is partner?

Have you checked partner is ok or not?

You can find so many modbus rtu sample application on Siemens support or forum.

Write small logic to get status information.

Move the MB Master/Slave status in other memory location while error bit is high.

Post the outcome of status code here ,so expert can suggest you necessary changes.

DJ_1

Hello,

Sorry but half information can get only half solution.

Which PLC version? Which software version? Is it MB Master or MB slave?

Who is partner?

Have you checked partner is ok or not?

You can find so many modbus rtu sample application on Siemens support or forum.

Write small logic to get status information.

Move the MB Master/Slave status in other memory location while error bit is high.

Post the outcome of status code here ,so expert can suggest you necessary changes.

 SW,TIA  V13 SP1
I am using CPU1214C, DC/DC/RLY, firmware 4.1.
CM1241 firmware is 2.1.

I used s7-1200 as a master can recevie data from different device.

But I used S7-1200 as a slave by using mb_comm_load and mb_slave and only receive bad_crc .

I tried to use modbus poll(third party software) through rs485/rs232 converter  to read data by using
function 03(read holding register), but still fail and the modbus poll said write error:break condition.

I struggling with this almost a week:(

sohaboss2016

 

DJ_1

Hello,

Sorry but half information can get only half solution.

Which PLC version? Which software version? Is it MB Master or MB slave?

Who is partner?

Have you checked partner is ok or not?

You can find so many modbus rtu sample application on Siemens support or forum.

Write small logic to get status information.

Move the MB Master/Slave status in other memory location while error bit is high.

Post the outcome of status code here ,so expert can suggest you necessary changes.

 SW,TIA  V13 SP1
I am using CPU1214C, DC/DC/RLY, firmware 4.1.
CM1241 firmware is 2.1.

I used s7-1200 as a master can recevie data from different device.

But I used S7-1200 as a slave by using mb_comm_load and mb_slave and only receive bad_crc .

I tried to use modbus poll(third party software) through rs485/rs232 converter  to read data by using
function 03(read holding register), but still fail and the modbus poll said write error:break condition.

I struggling with this almost a week:(

 Hello,

Now information looks good.

Let see Scenario,

S71200 acting as Modbus Slave. use Modscan software for testing.( Modbus Master)

As i suggested, 

Write small logic , while getting error bit of Modbus Slave block move the status in some other memory location. Then let us know the status code.

see the attached picture.

DJ_1

 

sohaboss2016

 

DJ_1

Hello,

Sorry but half information can get only half solution.

Which PLC version? Which software version? Is it MB Master or MB slave?

Who is partner?

Have you checked partner is ok or not?

You can find so many modbus rtu sample application on Siemens support or forum.

Write small logic to get status information.

Move the MB Master/Slave status in other memory location while error bit is high.

Post the outcome of status code here ,so expert can suggest you necessary changes.

 SW,TIA  V13 SP1
I am using CPU1214C, DC/DC/RLY, firmware 4.1.
CM1241 firmware is 2.1.

I used s7-1200 as a master can recevie data from different device.

But I used S7-1200 as a slave by using mb_comm_load and mb_slave and only receive bad_crc .

I tried to use modbus poll(third party software) through rs485/rs232 converter  to read data by using
function 03(read holding register), but still fail and the modbus poll said write error:break condition.

I struggling with this almost a week:(

 Hello,

Now information looks good.

Let see Scenario,

S71200 acting as Modbus Slave. use Modscan software for testing.( Modbus Master)

As i suggested, 

Write small logic , while getting error bit of Modbus Slave block move the status in some other memory location. Then let us know the status code.

see the attached picture.

 I tried the modbus_slave and this remain in status 8280.

Also,I used the mb_slave and status is 16#0000,only bad_CRC_COUNT is accumulated.

I am struggled in this stage for a long time...

Also, can the s7-1200 communicate with the modbus device by 8n2?

Hello,

very sry, now totally lost idea who is communicated with who. Can you pls again clearly give info about Master device and Slave device? Communication parameters we know, 9600/8/N/1. If Master is PC application, which type? Is used some adapter/converter?

danw

Since you already have the Modpoll 3rd party PC master, you might consider reading some non-zero data from the slave device so that you can observe whatever feedback (blinking LEDs) the RS-485 port has for the slave device and gain the confidence that the slave does indeed talk Modbus.   There are generally fewer things to set up or to go wrong with the generic masters, so it's easier to get the comm up and running.

Doing so can also tell you whether the addressing Modpoll uses is offset by one, where address 0032 = (4)0033

Look for a non-zero value because lots of slave devices zero out unused register so you might get a zero reply even though the data is from an address offset by one, and the real data is not zero.

If a Receive LED blinks, then the A/B wires are probably not crossed, but a common issue with RS-485 is that the A/B lines are labeled the opposite by different vendors.  Swapping the A/B lines on one end fixes it.   Backwards installation will not damage the line drivers, but communications will never work.

 After swapping A/B lines , the miracle occur!!!! I can use  modbus poll to get the data.

But when I perform other rtu 485 communication ,it's usually A1 to + ,B1 to -......
It's the bus connector problem?