Skip to Content

Register Login

Industry Online Support

Technical Forum

Navigation

CPU 921 S Processor Transmit data block (OB 255) Conversion to S7

Created by: melsec- at: 11/9/2010 7:17 AM (4 Replies)

Rating (1)

Thanks 2

5 Entries

11/9/2010 7:17 AM	Rate (0)
melsec- Experienced Member Joined: 6/14/2008 Last visit: 1/25/2022 Posts: 65 Rating: (3)	Hello I want to change CPU921 (6ES5921-3UA12) into S7-400. "OB255" was used by the program of CPU921. About OB255, since I knew nothing, I looked for the manual. SlMATlC S5 135 U Programmable Controller S ProcessorProgramming instructions Order No. C79000-B8576-C264-037 System program special functions7.1 Transmit data block (OB 255) . . . .91 There is little information of OB255 by this manual. I read the description. However, my understanding is lacking. OB255 is omitted in From S5 to S7 Converter Manual. I want those knowledgeable to help. Thank you
	Last edited by: melsec- at: 11/9/2010 7:19 AM
Suggestion To thank Quote Answer

11/9/2010 7:32 AM	Rate (0)
melsec- Experienced Member Joined: 6/14/2008 Last visit: 1/25/2022 Posts: 65 Rating: (3)	The contents of a program of CPU921 for which OB255 is used OB22 Segment 1 :STL :AN F0.7 :S F0.7 :AN F9.0 :S F9.0 :JU FB220 Name :DB-RAM :JU FB201 Name :KONSTANT :BE FB220 Segment 1 NAME:DB-RAM : L KB 20 :JU OB 255 <--- :C DB 20 :BE FB201 Segment 1 Name:KONSTANT :CDB 20 :L KB 0 :SLD 32 :L DW 10 :FDG :T DD160 :L KB 0 :SLD 32 :L DW 11 :FDG :T DD162 :L KB 0 :SLD 32 :L DW 12 :FDG :T DD 164 :L KB 0 :SLD 32 :L DW 13 :FDG :T DD 166 :L KB 0 :SLD 32 :L DW 14 :FDG :T DD 168 :*** Segment 2 :L KG +1021000+04 :L DD164 ::G :T DD 170 :L DD 162 :XG :T DD 172 :GFD :T DW 44 :L DD 164 :L DD 168 ::G :T DD 174 :BE

Suggestion To thank Quote Answer

11/9/2010 8:39 AM	Rate (0)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 11/28/2023 Posts: 2996 Rating: (1039)	Hello melsec- I presume you have an EPROM in your 921 CPU, correct? If so, the short answer is: Do not worry about OB255 and simply delete its call from the S5program. The background behind this advise is: A S5 921 CPU needseither a RAM or EPROM card to store the User program. To be able for the S5 program to store/write data into DB's, youhad to load the DB's upon PLC startup (e,g, OB22) from the EPROM into the inbuilt so called "Data Block RAM" of the CPU. This is what OB255 does in your logic and there is no need for it anymore in an S7 PLC. Just in case you have a RAM in 921 CPU, you can still safely delete the call (the most likely reason for using OB255 is now to free up memory on the RAM card by transfering the DB to the inbuilt DB RAM) I hope this helps
	Cheers fritz The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited. To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
Suggestion To thank Quote Answer

11/9/2010 9:36 AM	Rate (0)
melsec- Experienced Member Joined: 6/14/2008 Last visit: 1/25/2022 Posts: 65 Rating: (3)	Hello, Mr. fritz Thank you for giving a reply. I appreciate your help. ROM with which CPU is equipped does not understand whether they are EPROM or RAM. The file of a program and the photograph of CPU were passed. The photograph of CPU is appended.In which can it judge between EPROM and RAM from this photograph? Moreover, is it good about OB255 at the following interpretations? FB220 Segment 1 NAME:DB-RAM : L KB 20ß----Accumlator1-L:KB20/Accumlator1-H:KB0 :JU OB 255ß--- The contents of DB0 transmit to DB20 :C DB 20 :BE Attachment melsec.jpg (85 Downloads)

Suggestion To thank Quote Answer

11/10/2010 9:43 AM	Rate (1)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 11/28/2023 Posts: 2996 Rating: (1039)	Hello melsec- I can't say from the pic if it is a RAM or EPROM, you will have to "find" its part number to find out what type it is. Having said that (and as mentionedbefore), it doesn't really matter asyou do NOT needthe "OB255 functionality" in your S7, so simply delete its call (as well as the then surplus "L KB20") when converting. As for what your code exactly does, please see below: L KB 20 // DB Number thatis to be copied from (RAM or EPROM) User memory JU OB 255 //Copy DB20 from User memory to CPU internal DB-RAM I hope this helps
	Cheers fritz The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited. To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
Suggestion To thank Quote Answer
This contribution was helpful to 2 thankful Users melsec- AmirAlwaled

|

Share this page:

Share this page on...

Follow us on