Siemens and rs232 communications

Hi there,

At this moment i use mitsubishi PLC's with rs232 communication to a pc platform, a proces that reads and writes to the plc in so called "non protocol mode" , so the is no software programming in the PLC.

Is this also possible for Siemens ? ( CPU 314 and a CPU341 rs232 module )
Or is it always nessesary to make a program in the PLC that controles the RS232 port on the CPU 341 ?

If so, is there a site where i can find examples for RS232 communication ? i only need to read and write one or two datablocks.

Newbie on Siemens.

We use a similar system on one of our plants.
I don't know if it can communicate without protocol, since we send the data in modbus format. It also only sends a small amount of data at a time, so it takes 5-7 seconds to fully update.

This system is actually the least loved on our site.
We are currently setting up the system to communicate on Ethernet, which is how we have done the rest of our site. After that we will be burying all the old equipment at a cross roads somewhere with a large stone over it.

Hi,

5-7 second, thats way to long for us, we need speed, we have a proces of 50ms, and every cycle we need an update read and write, at this moment we use Mitsubishi, but the A-series, is at the end of its delivery cycle, and we can't use the Q-series, because of the lower I/O specifications. (current etc.)
So we are now looking at different PLC's and at this moment we have a test site with Siemens, but when i look in the manual for the RS232 communications, it looks like you always need some programming on the PLC side, so i was looking for some examples for reading and writing to a Datablock, this must have done before....

I am not sure how that non-protocol works, RS232 is just a wiring standard, not a protocol. It may be using ASCII, this link has an example for using ASCII.
http://support.automation.siemens.com/-snm-0135109872-1116758784-0000004488-0000001803-1121426836-enm-WW/llisapi.dll?filter=rs232&aktprim=0&func=cslib.csinfo&lang=en&nodeid0=10805148&objaction=csbrowse&objid=10805148&siteid=cseus&subtype=130000

I've done a lot of work with the CP340 and 341 cards, and you will need code in the PLC to send/receive data. The max speeds are dependent on the amount of data you are transferring in each message. If it is only 20 bytes or so, then 50ms is probably ok, but if the messages are in the hundreds of bytes, you will have to get creative.

Give us more detils and we'll help you out.

You can use Pre written Function Blocks to transfer your DB Values

See this thread for more details:

http://www.plctalk.net/qanda/showthread.php?t=15905

Download the manual and look a Section 2(serial transfer basics) and Section 9 (Programming examples)

Hope this helps

Steve

"No Protocol" mode on a Mitsubishi RS232 card means that you are not using a Mitsubishi protocol. This allows you to write your own serial port driver in the PLC programme. If you are using this mode there has to be some PLC code involved. If you can find this it should give you a good idea of what you need to do to duplicate the function on your new PLC.

S7Guy said:

I've done a lot of work with the CP340 and 341 cards, and you will need code in the PLC to send/receive data. The max speeds are dependent on the amount of data you are transferring in each message. If it is only 20 bytes or so, then 50ms is probably ok, but if the messages are in the hundreds of bytes, you will have to get creative.

Give us more detils and we'll help you out.

Click to expand...

Ok lets try to explain what we are doing with the PLC.

A "C" application on a pc platform controles the proces, with the RS232 port we write a "wanted" state to the PLC, and read back the real status of the PLC.
Also if there are some values that changes in the proces, we write that to the plc, so the PLC can work with these new values.
The PLC proces is based on a 100 mS scan, in this time there must be one write and read session, with the PLC.
The PLC checks if the "wanted" state of the Pc can be done, and if so, it will switch the outputs.

So i will need a Data block, where the Pc can write it's "wanted" state, and can read back the "real" state of the PLC.
And a Datablock (maybe the same ?) where we can exchange values (type word) with the Pc proces.
These values can also be changed with a HMI, so there are also a few bit's wich will indicate that the Pc platform needs to read back the values.

So I hope you now can imagine what the program is about, and what type of plc program for the Rs232 i will need.

Andybr said:

"No Protocol" mode on a Mitsubishi RS232 card means that you are not using a Mitsubishi protocol. This allows you to write your own serial port driver in the PLC programme. If you are using this mode there has to be some PLC code involved. If you can find this it should give you a good idea of what you need to do to duplicate the function on your new PLC.

Click to expand...

It's just the other way, in non protocol you don't have to write your own protocol, you can just take "mitsubishi" language, and read and write to the plc, without programming the PLC, the Rs232 card, writes and reads directly to the CPU inside the PLC.
So we only wrote the interface on the PC side.

Leonairo

I have used the Mitsubishi cards on many occasions and your description seems to be the wrong way round. the "No Protocol" mode always requires you to write PLC code to control the port. Connection to a SCADA system or similar can be done without any PLC code by using one of the four Mitsubishi protocols and a suitable driver on the PC. Most drivers tend to use Mitsubishi's type 1 protocol. If you want to duplicate this with the Siemens PLC you will need some kind of driver on the PC.

Andybr said:

Leonairo

I have used the Mitsubishi cards on many occasions and your description seems to be the wrong way round. the "No Protocol" mode always requires you to write PLC code to control the port. Connection to a SCADA system or similar can be done without any PLC code by using one of the four Mitsubishi protocols and a suitable driver on the PC. Most drivers tend to use Mitsubishi's type 1 protocol. If you want to duplicate this with the Siemens PLC you will need some kind of driver on the PC.

Click to expand...

You are totally right, it's protocol mode 1 , sorry for this confusion.

Andybr said:

Leonairo

I have used the Mitsubishi cards on many occasions and your description seems to be the wrong way round. the "No Protocol" mode always requires you to write PLC code to control the port. Connection to a SCADA system or similar can be done without any PLC code by using one of the four Mitsubishi protocols and a suitable driver on the PC. Most drivers tend to use Mitsubishi's type 1 protocol. If you want to duplicate this with the Siemens PLC you will need some kind of driver on the PC.

Click to expand...

You are totally right, it's protocol mode 1 , sorry for this confusion.