SLC 5/05 With SST Profibus Card M0 & M1

sticks99ca

Member
Join Date
Jul 2007
Location
Windsor, Ontario
Posts
7
Hello All,

I have an application using a SLC 5/05 processor with a SST profibus card. The application controls 10 servo drives and field bus devices that will be communicating over profibus. I'm looking into using only 1 SST card (32 input words & 32 output words) for controlling all 10 drives and field I/O. The drives will use approximately 120 total words.

My questions relates to the use of the M0 and M1 for drive information. Has anyone had any problems related to receiving/sending drive information and plc scan time? It's my understanding that receiving M0 and M1 data takes more time than I,O. I'm concerned about certain drive parameters not being immediately set or reset because of the longer communication times required for M0 and M1. Are there any issues I should to be aware of when using M0 and M1?

Thanks
 
We use profibus on some of our systems that control 4 drives and well over a 100 critical time valves and have never had any problems as far as communications speed. The mapping M0/M1 can be a bit of a pain to figure out at first but after that no problems.
 
Each access of the M0 or M1 file costs about 2 milliseconds of SLC controller scan time, no matter how much data is accessed.

I always use one COP instruction to get the M1 input data into an Integer buffer file, and another COP instruction to send an Integer buffer file to the M0 output data.

I recently saw a system where the programmer addressed bits in the M0 and M1 files individually, and his scantime was around 50 milliseconds.. Migrating his references to buffer files and using only two COP instructions cut the scantime to 16 milliseconds average.
 
sticks99ca said:
My questions relates to the use of the M0 and M1 for drive information.
No

Has anyone had any problems related to receiving/sending drive information and plc scan time?
It's my understanding that receiving M0 and M1 data takes more time than I,O.
It takes about 1 millisecond just to access the M files. Therefore do it only once per scan. SLC5/05s may be faster.

I'm concerned about certain drive parameters not being immediately set or reset because of the longer communication times required for M0 and M1. Are there any issues I should to be aware of when using M0 and M1?
Again, minimize the number of times you access the M files per scan. It takes a long time just to access the M files but not much time to transfer each register.

The M file memory is shared between PLC and the SST CPU. There is some handshaking that goes on. Once the PLC gains access it transfers all the data at once and then releases access to the M files.
 
Thanks for the feedback.

I have a question regarding sending/receiving M0/M1 data. When using the COP instruction does the PLC wait at that instruction until the data has been transfered? Will the next rung after the COP instruction have the new M1 data? Is there a specific handshaking bit to indicate when the data has been sent/received?
 
"Each access of the M0 or M1 file costs about 2 milliseconds of SLC controller scan time, no matter how much data is accessed."

So there is virtually no difference in time between reading 5 words vs. 50 words? It seems a little hard to believe that the amount of accessed data has no affect on scan time.
 
sticks99ca said:
So there is virtually no difference in time between reading 5 words vs. 50 words? It seems a little hard to believe that the amount of accessed data has no affect on scan time.

A SLC5/05 should be faster than that. I have seem manuals with the specifications on tha access time and the time per register. The access time is very large relative to the time to copy each register.
 
sticks99ca said:
Hello All,

I have an application using a SLC 5/05 processor with a SST profibus card. The application controls 10 servo drives and field bus devices that will be communicating over profibus. I'm looking into using only 1 SST card (32 input words & 32 output words) for controlling all 10 drives and field I/O. The drives will use approximately 120 total words.

My questions relates to the use of the M0 and M1 for drive information. Has anyone had any problems related to receiving/sending drive information and plc scan time? It's my understanding that receiving M0 and M1 data takes more time than I,O. I'm concerned about certain drive parameters not being immediately set or reset because of the longer communication times required for M0 and M1. Are there any issues I should to be aware of when using M0 and M1?

Thanks


Did you get this working? I'm trying the same and having a hard time figuring out the M0/M1 files...
 
tomalt said:
Did you get this working? I'm trying the same and having a hard time figuring out the M0/M1 files...
I found a document on the allen bradley site which listed the access and transfer times of the M0 and M1 data. For a SLC 5/05 processor the access time for using the COP to M file is 735 microseconds plus 23 microseconds per word. The COP from M file is 722 microseconds plus 22 microseconds per word. This time is added to the program scan time.

I haven't seen the practical results of using the 198 words M0 and M1 data because I'm still in the process of writing the software. But the addition time added to the PLC program scan time is approximately 5.905 milliseconds.
 

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