MODBUS RTU Hardware configuration - S7300

[naturephoenix]

Hi,

I got two questios:
There are two slave devices(SEL-787) from which I should read data via MODBUS RTU.
I checked SEL-787 manual and it says it supports EIA -232 , but my collegue order
"
6S7 341-1CH00-0AE0
Communication processor with connection: RS422/485 (RK512, ASCII, 3964(R), loadable driver)
"
Should we change order to:
"
6ES7 340-1AH02-0AE0
Communication processor with connection: RS232C (ASCII, 3964R, printer); V1.0
"

 

[gclshortt]

Modbus RTU is a serial communication.
Typically RS232 is a 1:1 communication. This means one master and one slave. Maximum cable length is usually 15m.
Typically RS422(4wire)/RS485(2wire) is a 1:N communication. This means one master and several slaves (256). Maximum cable length is usually 200m.
Since you have two slaves and one master I would use RS485.

Hope this helps you out.
Regards,

 

[mk42]

I don't know much about that device, but when I looked at the spec sheet, it says it can support either 232 or 485.

My understanding is that Modbus RTU requires RS485.

Note that on the S7-300 side you need to buy a license for the modbus communications blocks, and they are not cheap.

It looks like the device also supports a number of ASCII modes, that might be a cheaper way to go (probably 232 OR 485).

 

[Lare]

I don't know much about that device, but when I looked at the spec sheet, it says it can support either 232 or 485.

My understanding is that Modbus RTU requires RS485.

Note that on the S7-300 side you need to buy a license for the modbus communications blocks, and they are not cheap.

It looks like the device also supports a number of ASCII modes, that might be a cheaper way to go (probably 232 OR 485).

Modbus RTU can be RS232 or RS485. Siemens modbus licenses isn't cheap.
Cheaper could be to use 1200 CPU with RS-card for modbus or IM151-8 CPU which don't need seperate license dongles. Then read from 1200 CPU data to 300/400CPU with profibus or net.
It is also possibly to connect ET200S or ET200SP PtP card to 300CPU with IM-card.

http://www.plctalk.com/qanda/showthread.php?p=464232

 

[naturephoenix]

Modbus RTU can be RS232 or RS485. Siemens modbus licenses isn't cheap.
Cheaper could be to use 1200 CPU with RS-card for modbus or IM151-8 CPU which don't need seperate license dongles. Then read from 1200 CPU data to 300/400CPU with profibus or net.
It is also possibly to connect ET200S or ET200SP PtP card to 300CPU with IM-card.

http://www.plctalk.com/qanda/showthread.php?p=464232

Hi,

I checked, cheapest s7-1200 CP1211C would be 132€
and CM ->6ES7241-1CH32-0XB0 91€

So thats all I need? no any additional licence payment or something what usually goes with Siemens?

 

[Lare]

Hi,

I checked, cheapest s7-1200 CP1211C would be 132€
and CM ->6ES7241-1CH32-0XB0 91€

So thats all I need? no any additional licence payment or something what usually goes with Siemens?

S1200 should be license free for modbus. Of course you need to make S1200 program and communications to modbus and read data then from 1200 to CPU300/400 with profinet comms.


If you wan't only use CPU300, then it also possible that you use license free ET200S or ET200SP PtP cards with 300CPU instead of IM151-8 or 1500CPU. Lot of choices.


For this you need IM151-1 or IM151-3 (remote IO) unit and PtP card 138-4DF11-0AB0 (ET200S I/O) or if you use ET200SP IO then you need IM155-6 (profibus or Profinet) and PtP card 137-6AA00

They are little bit more expensive but lot less cheaper than modbus license for old 340 serial card.
For ET200s there was also step7 example on Siemens Site.

https://support.industry.siemens.co...he-serial-interface-et200s-1si?dti=0&lc=en-WW



For ET200SP there is also example, but that was only for TIA portal and 1500CPU.

https://support.industry.siemens.co...-using-the-modbus-rtu-protocol?dti=0&lc=en-WW

(Have used both with 300CPU and step7 5.5, but needed code pretty much before it worked. Manual was little bit less than 100 pages

S1200 modbus look easy to code (ready blocks), have never used that for real environment thought. It have same princibles that ET200SP PtP.

https://support.industry.siemens.co...rtal)-for-the-simatic-s7-1200-?dti=0&lc=en-UY

 

[naturephoenix]

S1200 should be license free for modbus. Of course you need to make S1200 program and communications to modbus and read data then from 1200 to CPU300/400 with profinet comms.


If you wan't only use CPU300, then it also possible that you use license free ET200S or ET200SP PtP cards with 300CPU instead of IM151-8 or 1500CPU. Lot of choices.


For this you need IM151-1 or IM151-3 (remote IO) unit and PtP card 138-4DF11-0AB0 (ET200S I/O) or if you use ET200SP IO then you need IM155-6 (profibus or Profinet) and PtP card 137-6AA00

They are little bit more expensive but lot less cheaper than modbus license for old 340 serial card.
For ET200s there was also step7 example on Siemens Site.

https://support.industry.siemens.co...he-serial-interface-et200s-1si?dti=0&lc=en-WW



For ET200SP there is also example, but that was only for TIA portal and 1500CPU.

https://support.industry.siemens.co...-using-the-modbus-rtu-protocol?dti=0&lc=en-WW

(Have used both with 300CPU and step7 5.5, but needed code pretty much before it worked. Manual was little bit less than 100 pages

S1200 modbus look easy to code (ready blocks), have never used that for real environment thought. It have same princibles that ET200SP PtP.

https://support.industry.siemens.co...rtal)-for-the-simatic-s7-1200-?dti=0&lc=en-UY

Let's say I choice S7-1200 with CM for modbus,
Rest is transfering data from S7-1200 to S7-300.
That should be possible with PUT and GET functions?

 

[mk42]

Let's say I choice S7-1200 with CM for modbus,
Rest is transfering data from S7-1200 to S7-300.
That should be possible with PUT and GET functions?

Put and Get, or T_Send/Recv would be the way to do it acyclicly.

Make the 1200 an I-device to the 300 (Profinet), would be the way to do it cyclicly.

 

[Lare]

PUT / GET work. Make unspefied or specified connection.
If you use unspecific, then project can be on different files and S1200 only needs couple DB-blocks. (DBs where you write and read from)

On master side you configure partner IP to NetPro(S1200) and use communication ID (hex-code) for PUT/GET.

 

[naturephoenix]

Thx all for making ti clear to me which hardware I should be used for modbus rtu in order to get it for lowest price!!!

What about Modbus TCP/IP

Is there also solution with s7-1200 and some CM?

 

[mk42]

Thx all for making ti clear to me which hardware I should be used for modbus rtu in order to get it for lowest price!!!

What about Modbus TCP/IP

Is there also solution with s7-1200 and some CM?

no CM needed for modbus TCP, the 1200 has an Ethernet port built in. However, you can use a CM if you need it to be on a different subnet (isolated from the rest of the network).

 

[naturephoenix]

no CM needed for modbus TCP, the 1200 has an Ethernet port built in. However, you can use a CM if you need it to be on a different subnet (isolated from the rest of the network).

Yes ethernet port is built in, but MODBUS TCP/IP Master and slave are supported too?

 

[Lare]

It is supported. You need only code it to use with FB blocks.
Serial and TCP have own blocks.

 

[naturephoenix]

It is supported. You need only code it to use with FB blocks.
Serial and TCP have own blocks.

So no any additional licence payment is needed?

When you say code it, do you mean to "make a MODBUS message"(fprmat message by observing modbus rules ) or just
use SIEMENS functions for SEND and RECEIVE(MODBUS Mesaage is done by siemens already)

 

[Lare]

I mean that on S1200 you need to use only Siemens allready maded FB-blocks. Only thing you need take care is sequence read/writes on serial. (and TCP if there is lot of read/write)

For TCP there is Client and Server blocks.
You only need to tell to these IP address, DB-area of modbus and on Writing to Modbus slave start address (0x,1x, 3x and 4x style) and how many addresses.

Modbus querys are then maded at behind, it can't be much easier on Siemens this time.
(Comparing to ET200S series, you need to use Send/Recv blocks and know little bit more of modbus)



https://support.industry.siemens.co...tion-between-two-s7-1200-cpus-?dti=0&lc=en-WW

https://support.industry.siemens.com/cs/mdm/109741593?c=89566476555&lc=en-WW

and S1200 system manual, from page 624.

https://support.industry.siemens.co...7-1200-programmable-controller?dti=0&lc=en-WW