Portal | Manuals | References | Downloads | Info | Programs | JCLs | Mainframe wiki | Quick Ref
IBM Mainframe Computers Forums Index
 
Register
 
IBM Mainframe Computers Forums Index Mainframe: Search IBM Mainframe Forum: FAQ Memberlist Profile Log in to check your private messages Log in
 
Index register concept in RX type instruction format

 
Post new topic   Reply to topic    IBMMAINFRAMES.com Support Forums -> PL/I & Assembler
View previous topic :: :: View next topic  
Author Message
sheersh

New User


Joined: 24 May 2008
Posts: 15
Location: Gurgaon

PostPosted: Sat Sep 20, 2008 10:23 pm    Post subject: Index register concept in RX type instruction format
Reply with quote

Please help me understanding Index register concept in RX type instruction format.

Is this something, base register is pointing to some register(Index register) and then calculating the offset to reach memory location?

Is this something we can achieve or depends upon system's memory organization? bit confused, please help.
Back to top
View user's profile Send private message

CICS Guy

Senior Member


Joined: 18 Jul 2007
Posts: 2150
Location: At my coffee table

PostPosted: Sat Sep 20, 2008 11:48 pm    Post subject: Re: Index register concept in RX type instruction format
Reply with quote

sheersh wrote:
Is this something, base register is pointing to some register(Index register) and then calculating the offset to reach memory location?
Base, index and displacement are all added together....
z/Architecture Principles of Operation wrote:
In forming the intermediate sum, the base address and index are treated as 64-bit binary integers. A 12-bit displacement is treated as a 12-bit unsigned binary integer, and 52 zero bits are appended on the left. A 20-bit displacement is treated as a 20-bit signed binary integer, and 44 bits equal to the sign bit are appended on the left. The three are added as 64-bit binary numbers, ignoring overflow. The sum is always 64 bits long and is used as an intermediate value to form the generated address. The bits of the intermediate value are numbered 0-63.
Back to top
View user's profile Send private message
Bill Dennis

Active Member


Joined: 17 Aug 2007
Posts: 562
Location: Iowa, USA

PostPosted: Tue Sep 23, 2008 12:25 am    Post subject:
Reply with quote

Base register points to an area in memory.

Displacement value is added to BASE to point to a specific field.

Index value, in a second register, is added to the BASE and displacement usually to locate a specific byte within a field. Increasing the Index by 1 is handy for looping thru a field looking for certain strings.
Back to top
View user's profile Send private message
View previous topic :: :: View next topic  
Post new topic   Reply to topic    IBMMAINFRAMES.com Support Forums -> PL/I & Assembler All times are GMT + 6 Hours
Page 1 of 1

 

Search our Forum:

Similar Topics
Topic Author Forum Replies Posted
No new posts Fetch Previous month & year in MM... girishb2 DFSORT/ICETOOL 3 Thu Sep 21, 2017 9:54 pm
No new posts Setting Font Type for XMIT satish.ms10 All Other Mainframe Topics 3 Fri Sep 15, 2017 10:01 pm
No new posts Convert rows and column into JSON for... Dinesh Manivannan DB2 2 Sun Sep 03, 2017 6:50 pm
No new posts Confusion b/w index and subscript Deepak kumar25 Mainframe Interview Questions 7 Thu Aug 31, 2017 6:50 am
No new posts Updating the Trailer count in variabl... satheshbabur DFSORT/ICETOOL 6 Wed Aug 30, 2017 9:49 pm

Facebook
Back to Top
 
Job Vacancies | Forum Rules | Bookmarks | Subscriptions | FAQ | Polls | Contact Us