IBM Mainframe Forum

by **dick scherrer** » Sun Nov 21, 2010 10:41 pm

Hello,

but I guess there is a reason for it.

Yes, because after "it" comes out of the box, people get their hands on "it"

Actually, there are many different products and tools available which leads to some dis-similarity. Additionally, some organizations have more structure to their environment. Many create their own tools to meet requirements beyond the vanilla system as it comes out of the box.

After several environments, the "next" one is easier. . .

by **stevexff** » Mon Jan 17, 2011 4:49 pm

From my own personal experience, the biggest hurdle was understanding register based addressing; once I'd got my head round that it all fel into place, and the rest was just learning about the various instructions. The Principles of Operation does a great job of describing the what each machine instruction does in excruciating detail. What it is less good at is describing what they should be used for, and under what circumstances...

by **alexlloyd54** » Tue Jan 18, 2011 6:16 am

IBM manuals are not a good start if you want to learn Assembly language from scratch, they are meant to be used as a reference

there are a lot (or few) of books regarding assembly language, and i recommend the following:

1) Structured Assembly Language programming for the IBM 370 (by James Silver) ISBN 0-02-411040-x

it's one of the best books, though it's too old and it might be difficult to find :shock:

2) Advanced Assembler Language and MVS Interface (by Carmine Cannatello) ISBN 0-471-36176-3

and of course, don't forget to get a copy of the IBM (Principles of operation) manual as a reference.

The most important thing is to give yourself a lot of time, and the most important ... to love the language

good luck

by **steve-myers** » Tue Jan 18, 2011 6:58 am

Personal opinion: it really helps if you are reasonably proficient in a mid-level language, like C. Assembler is not so good as a first language.

Two other manuals are Using Datasets and Macro Instructions for Datasets. The links are for z/OS V1R12, but the material changes very slowly. Using Datasets is somewhere between a reference and a text. Macro Instructions for Datasets is strictly a reference.

Assembler Services Guide and Assembler Services Reference 1 and Assembler Services Reference 2 are also manuals you'll need. The IBM Assemblers have always had an extremely powerful macro language, so all the operating system interfaces are accessed through the macro language rather than through the the System/360 equivalent of the INT instruction. ESA/370 introduced what amounts to the call gate interface in 80x86 PC hardware; some of the macros use that interface.

by **steve-myers** » Tue Jan 18, 2011 12:07 pm

By its nature, Assembler is not a "structured programming" language. Something like 30 years ago, my good friend Bill Mosteller wrote a book called "Systems Programmer's Problem Solving Guide." It's been out of print for something like 25 years, and much of its advice is outdated by now, but there was one very important comment about "structuring" Assembler code that goes a long way toward making your code easier to understand:

Do not insert a branch to a lower storage location except to form a loop.

After I thought about it I realized I'd been mostly following Bill's advice anyway; since then I've followed his advice fairly religiously.

by **alexlloyd54** » Mon Jan 24, 2011 8:39 am

Steve

the poster is new to Assembly programming, most of the manuals that you've mentioned are too advanced for him

I think he should start with the "Hello World" program first (simple read & print)

then would start doing some data manipulation ... etc etc

later when he finds himself capable to go further, he would start reading about macros and system services.

when someone wants to learn how to drive, he would NEVER start with an expensive car

by **steve-myers** » Mon Jan 24, 2011 10:56 am

I started doing Assembler for IBM 7040 IBSYS. I did start relatively "simple" in '65, but advanced fairly quickly.

I started OS/360 Assembler in '68. As with 7040 I tried "simple" stuff first, and advanced to more complex stuff rather less quickly than with 7040. As with the 7040 numeric conversions were somewhat difficult. One project in early '69 I still recall with pride was to build a macro set that linked to the Fortran library for reading and writing. The macro set would build "compiled" Fortran formats.

Your proposed Hello World program requires "simple" macros like SAVE and RETURN, as well as some of the "simpler" I/O facilities like OPEN, CLOSE, PUT, and the base parts of the dreaded DCB macro.

Select all

WORLD CSECT DEFINE PROGRAM CSECT
USING *,12 SPECIFY PROGRAM ADDRESSABILITY
SAVE (14,12),,* SAVE REGISTERS
LR 12,15 COPY ENTRY POINT ADDRESS TO REG 12
LA 15,SAVEAREA LOAD ADDRESS OF THE NEW SAVE AREA
ST 15,8(,13) ADD THE NEW SAVE AREA TO THE
ST 13,4(,15) SAVE AREA CHAIN
LR 13,15 ESTABLISH THE NEW SAVE AREA POINTER
OPEN (PRINT,OUTPUT) OPEN SYSPRINT
PUT PRINT,HITHERE WRITE HELLO WORLD
CLOSE PRINT CLOSE SYSPRINT
L 13,4(,13) LOAD ADDR OF THE PREVIOUS SAVE AREA
RETURN (14,12),T,RC=0 RESTORE REGISTERS AND RETURN
SAVEAREA DC 9D'0' NEW OS/360 SAVE AREA
PRINT DCB DSORG=PS,MACRF=PM,DDNAME=SYSPRINT,RECFM=FBA,LRECL=121
HITHERE DC CL121' HELLO WORLD!'
END WORLD

by **sensuixel** » Tue Feb 22, 2011 3:26 pm

I started HLASM four month ago with a classic "HELLO WORLD"

Then I read Principle of operation one instruction at a time (started with L, LA, MVC then B,BZ ...).

I quickly bookmarked http://csc.colstate.edu/woolbright/WOOLBRIG.htm which helped me a lot to understand adressing, linkage
and numeric conversion.
This link http://stevenscs.com/notes/HLASM/HLASM.Notes.html was also helpful to understand the basics.

On this basis, I've coded simple program as counting record from file and write the result with WTO or in a file in LOCATE mode or MOVE mode ...

Recently i bought Advanced Advanced Assembler Language and MVS Interfaces, it content a lot of sample and give hint to code properly.
Now i spend more time on principle of operation, IBM HLASM Language reference and IBM HLASM Programmer's guide.

Good luck

by **steve-myers** » Sat Feb 26, 2011 3:33 am

stevexff wrote:From my own personal experience, the biggest hurdle was understanding register based addressing...

I came into System/360 from 7040. The concept of base register / displacement addressing was somewhat new, though it was theoretically possible in 7040 it was rarely used. IBM 704/709/704x/709x normally addressed storage by having one or sometimes two 15 bit addresses in each 36-bit instruction. I quickly understood the advantages of the System/360 addressing and 16 registers compared to 2 registers and 3 15-bit "index" registers on the 704x. What I had trouble with, at first, and it still gives me trouble after 40+ years is matching the 4-bit mask in BC instructions with the 2-bit condition code set by many instructions. Thank goodness for extended branch mnemonics!

by **David Woolbright** » Wed Aug 17, 2011 8:42 am

My IBM assembler web site address has changed to http://csc.columbusstate.edu/woolbright/WOOLBRIG.htm
I am in the process of recording video lectures for an introductory course in assembler. I have posted a few of the lectures on the site already, so you can get an idea of what I'm up to. I'll be teaching assembler in the spring and I will finish recording the rest of the lectures by next May 2012.

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