Assembler - CONTENTS 1. Introduction 2. Basic Concepts 3....

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CONTENTS 1. Introduction 2. Basic Concepts 3. Instructions 4. Symbols, literals, expressions, Constants and data areas, location counter 5. Integer operations 6. Decimal operations 7. Data transfer and Logical operations 8. Bit manipulations 9. Branching 10. Assembler Directives 11. JCL aspects 12. Subroutines, linkage 24 bit mode 13. Mixed Mode Programming using COBOL and Assembler .
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INTRODUCTION back What is Assembly Language Lowest-level of programming on a system Symbolic forms of representing machine language instructions Usually represents a single machine instruction Machine dependent Advantages over high-level language 1* Very efficient and tight code can be developed Disadvantages 2* Applications development time is more 3* Applications are machine dependent 4* Relatively more difficult to learn and understand than a high level Language Advantages over machine language 5* Use of mnemonic operation codes helps remembering the instructions 6* Symbols can be used to represent variables and constants 7* Macros can be used to generate repeated codes 8* Conditional assembly enables tailoring the code generated
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BASIC CONCEPTS back IBM-370 MACHINE ARCHITECTURE 1* Main storage Addressed by 24 bits or 31 bits 2* One single address space contains code and data 3* Byte is the least addressable unit 4* Instruction categories 9* Fixed point Arithmetic, 10* Decimal Arithmetic, 11* Floating point Arithmetic, 12* Logical Operations, 13* Branching, 14* Status Switching, 15* Input Output 5* Programmer accessible Hardware Registers are 16* Program Status Word (PSW) 64 bits wide 17* General Purpose Registers (GPRs) 18* Floating Point Registers (FPRs) 19* Control Registers (CRs) 0-15 each 32 bits wide 20* Access Registers (AR'S) 0-15 each 32 bits wide 6* PSW 21* 64 bits in length 22* Contains the Condition Code (two bits) 23* Address of the next instruction to be executed. 24* PSW Key field 7* GPR'S 25* numbered 0-15 and 32 bits wide 26* Used as accumulators in Fixed point arithmetic 27* Used as base and index registers in computing the effective address 28* Two consecutive registers can be used to hold 64bit operands addressed by even register 8* AR'S 29* Numbered 0-15 each 32 bits wide 30* Used to point to address / data space 9* FPR 31* Used for floating point operations 32* Numbered 0,2,4,6 each 64 bits wide 33* 64 bits in length 34* Can contain short or long operand 35* Two adjacent registers can be used as 128 bit register for extended precision 10* CR'S 36* Control registers each of 32 bits are available 37* Used by the IBM control program 38* Instructions to access / modify them are privileged and can be issued only by the OS. 11* INPUT/OUTPUT 39* Data processing and I/O processing are concurrent 40* Consists of Channel subsystem, Control Unit and I/O unit
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ASSEMBLY STATEMENT FORMAT 1 10 16 72 12* Fixed Format. Can be changed only through ICTL Assembler Directive 13* Fields in a statement are separated by one or more blanks 14* Name / label field if present must start in column 1 and maximum 8 characters in length
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Assembler - CONTENTS 1. Introduction 2. Basic Concepts 3....

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