PLC-Writing onto the PC CPU after CPU is stopped

Hi,
I am developing a software to backup and restore the plc programs using TCP/IP communication. The etherneT interface module of the PLC is A1SJ71E71-B2-S3. I could backup the main sequence program but could not restore it. According to the manual SH-NA-3598-C, I should stop the CPU before writing to it. I could stop the CPU but could not write to it as the tcp/ip connection is gone ans so cannot communicate. Can you please help as how to open the PLC communication line ?

Hi fatema,

what PLC type are you talking about ?

Possibly, it is not a shutdown (power off) that is meant by "stopping" the CPU. It is more likely to be to put it in program mode.
This will stop the program in the CPU from running, but keep the CPU alive and hence also its communication ports.

Thanks for the reply, Jasper.

I am using A Series PLC from Mitshubishi. The CPU is A1S. Actually, I am new to PLC programing and am more towards object oriented programming so please help me.

Regards,
Fatema.

When you read from a PLC, it does not need to go into "Program " mode. You just read the internal files/registers.

To write to it you could have to put it into "Program " mode but many permit writing in "Run " mode. Its called "On-line edit ". You must have the "Source code " exactly matching what is already in the PLC to do it.

To write a value into an internal register, you can use some of the available com protocol or build your own but to read the "Compiled " logic program I thinck you have a real big job in front of you.

Good luck young one .

Only the young have this kind of time to spare to accomplish such task

Sorry Fatema, but I an expert in neither Mitsubishi, nor in writing/reading to the code area of PLCs. This is specifik know-how that the PLC manufacturers keep to themselves.

To write/read from the data areas of various PLCs is another matter. The PLC manufacturers have various open and propriatery solutions to do this. I think that the manual is referring to writing to the data area.

I guess, that when a some third party develops programming software for the PLCs, they use "snoopers" to listen to the original manufacturers programming softwares comminication with the PLCs. In that way they can learn both commands and code formats.

It is no little quest that you are setting out on. I cant help you more on this one.
Good luck

Hi Jasper,

My task is to read the main sequence program from PLC CPU and backup into the database. I could do the backup successfully. More maintenance purpose, there could be the need to restore it back and so write the same program back onto the CPU. I have the protocol to write the same program back but the response code received indicates that one should stop the CPU as the program could be running and then write to it. There is a command to stop the CPU , not physical stop I guess. But the problem is the TCPIP connection is lost.
I do not know this part,How to retrieve the communication back and so cannot understand what actually the CPU stop command is doing. My Java program as a Client, cannot communicate to PLC which opens a server side socket for the communnication. Can you please suggest as how to proceed further ?

Fatema

I use Mitsi PLC's a lot, however i've never used the TCP/IP module. In the A-series though i would assume that when you stop the PLC you also stop all special function modules, including the TCP/IP module. I would have a serious talk with the tech support guys at mitsubishi as i am not sure you can remotely program the PLC from a TCP/IP module unless the module can be kept running while the PLC is stopped. It seems silly to me that this cannot be done so i, sorry but again, guess that there is a mode to keep the TCP/IP module running while the PLC is stopped. I would ask the people at Mitsi about this.

I'm sorry i can't be that much of a help

Thanks Jasper.

Thanks Xion

Fatema

I've been using ethernet modules on Q and QnA but never needed to write to
stopped PLC. I do remeber reading something about it in a
manual but didn't have time to try it out. Unfortunatelly
you won't get much help on this subject unless you speek
Japaneese and work night shifts. You are pretty much on your own
since tech support is not good even for much simpler things with Ethernet card.
Two years ago they were shocked when I called to ask about
few things about little ethernet card for Q.

I was using IB_NA_66661_F manual (it's for QnA CPUs).
Chapter 16 describes communication with stopped CPU.
I would post it here but the manual is huuuuuuge (almost 40MB)!
BTW. chapter 16 is only three pages.
Anyway, before you can write, you have to setup ethernet card to
work like you want it. See buffer register 103 (67h) and read
about Y19 (you will need to setup dipswitches on the card).

Hope this helps