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S5-95U memory address

Created by: Ryszard_K at: 3/20/2013 5:48 PM (6 Replies)

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3/20/2013 5:48 PM	Rate (0)
Ryszard_K Posts: 7 Rating: (0)	Hallo! I have questions about RAM Address Assignment in S5-95U. In manual i read, that from 7E00h to 7FFFh is address list of DB. My question is: 1. Is in this area DB0 only? 2. What is the structure DB0? 3. In witch area was located user defined DB (DB2 ... 255)? I try to understend LIR and TIR instuctions. I hope these answers will help me. Thank you in advance for your help.
Ryszard_K Posts: 7 Rating: (0)
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3/23/2013 1:16 PM	Rate (2)
jklm Platinum Member Joined: 12/22/2006 Last visit: 1/25/2022 Posts: 1742 Rating: (309)	Hello, Data block DB 0 contains a list with the start addresses of all blocks in the user memory of the CPU. The system program generates this list after power up andupdates it automatically when you use a programmer to enter or change blocks. DB0 contains 256 entries for each block Type (OB, PB, ...). The zone starting with7E00 is the one listing the start addresses of the Datablocks in the user memory. In a 95U the memory is organized bytewise, but an address that points to a given byte is 16 bit long (and occupies 2 bytes). So each entry is a word wide and is an absolute address that points to the firstbyte after theblock header (for datablocks is that DL0 of that DB). Knowing this, you can now compute the absolute address of a dataword in the RAM of the CPU. And access that value with an indirect load (LIR) Major Steps: - You first take 7E00, you add the number of the datablock2 ==> address of the pointer in DB0. - You fetch the content of that address using LIR0, and you get the address of DL0 of that DB in Accu1. - Now you add the number of the DW that you want to fetch2 ==> address of the DW And you fetch it with LIR0 to get the value in Accu 1 TIR allows the reverse operation TNB allows to copya range of bytes from one location to another.
	Best regards jklm Suggestion was helpful? Feel free to rate it.
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3/23/2013 11:37 PM	Rate (0)
Ryszard_K Posts: 7 Rating: (0)	Hi jklm. Thank you very much for your response to my two posts. I realized that the data blocks are located above the address 7FFFh and DB0 is indicated address of the youngest byte in the DB. I'm right? Whether it should be understood that the header is the area just before the address indicated in the DB0? What is the structure of the DB header? Best regards. I'm sorry that my English is not good enough.
Ryszard_K Posts: 7 Rating: (0)
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3/24/2013 9:45 AM	Rate (1)
jklm Platinum Member Joined: 12/22/2006 Last visit: 1/25/2022 Posts: 1742 Rating: (309)	Hello, I expect the content of the DBs (the effective data) to be located in the program memory in adresses between 0100h and 40FFh. The DB entries of DB0 points to the memory mocation of the very first useful data byte(DL0 = data left 0 = left part of DW0) in each data block. Each block has an header of 5 words (10 bytes) that are not from interest normally for the user.
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3/24/2013 1:40 PM	Rate (0)
Ryszard_K Posts: 7 Rating: (0)	Hallo. Thanks for yoyr reply. I saw in some exaple loading to ACCU1 value from DBn word DW0 - 2. It is probably last (5th) word in header. What is in this word? Best regards Ryszard
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3/27/2013 8:10 AM	Rate (1)
KaOst Posts: 17 Rating: (2)	Hi! This is the 928B handbook, but the headers are equal in the 95Us. NB! I'm not sure of the length in word 5 (could be bytes in your 95u). See chapter 8.3.1 and onwards in the 928B manual in this link: http://support.automation.siemens.co...ew/de/19397726 KaOst
KaOst Posts: 17 Rating: (2)	Last edited by: KaOst at: 3/27/2013 8:11 AM
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3/28/2013 12:24 PM	Rate (0)
Ryszard_K Posts: 7 Rating: (0)	Hi jklm & KaOst Thank you for your response. It helped me to understand the code. Best regards Ryszard
Ryszard_K Posts: 7 Rating: (0)
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