Assembler/Session 1
Course Title :
ASSEMBLER LANGUAGE
Duration
CTS-PAC
: 5 Half - DAYS
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Assembler/Session 1
Objectives
Objectives
• Familiarize with IBM 370 Assembly Language
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Assembler/Session 1
COURSE SCHEDULE
SESSION 1
Day 1
Introduction
SESSION 2
Day 1
Addressing
SESSION 3
Day 2
CTS-PAC
Machine Instructions
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Assembler/Session 1
COURSE SCHEDULE
SESSION 4
Day 3
Program Sectioning
SESSION 5
Day 3
Assembler Directives
SESSION 6
Day 3
Writing a complete program
SESSION 7
Day 4
Assemble and link program
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COURSE SCHEDULE
SESSION 8
Day 4
SESSION 9
Day 5
CTS-PAC
Macro Language
Other Topics
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Assembler/Session 1
Assembler Language
SESSION 1
CTS-PAC
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Assembler/Session 1
Objectives
INTRODUCTION
• An assembler language is a symbolic form of
machine language
• Assembler translates assembler language
program to machine language
• An assembler program consists of many
statements
• In general, one assembler language statement
corresponds to one machine language
instruction
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Assembler/Session 1
STATEMENT FORMAT
1
label
10
operation
e.g..
INIT1
Objectives
LA R5,4
16
operands
30
comments
;INITIALISE REGISTER 5
Rules for choosing labels:
• maximum 8 characters
• Alphabets, digits, @, #, $
• First character should not be a digit
• label should begin in column 1
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Assembler/Session 1
Col1
…..
…..
A
B
ANS
CTS-PAC
Objectives
Sample program
Col10
Col.16
L
A
ST
2,A
2,B
2,ANS
DC
DC
DS
F’15’
F’20’
F
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Assembler/Session 1
STATEMENT FORMAT
Objectives
Operation
• One of the 200 M/C instruction mnemonics (eg. MVC)
Operand
• can be a register or memory location
Continuing a statement
• Place any character in column 72 of the line to be continued
• Continue the statement from column 16 of next line
• Maximum 2 continuation lines for a statement
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Assembler/Session 1
STATEMENT FORMAT
Objectives
Comment Statement
• * in column 1
• Any text in columns 2 - 71
Note : Fields separated by one or more
blanks
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TYPES OF INSTRUCTIONS
Objectives
1. Machine Instructions
2. Assembler Instructions (Directives)
3. Macro Instructions
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REGISTERS
Objectives
Registers are storage areas inside the processor
Advantages:
- No need to retrieve data from main storage
(saves time)
- Shared resource that allows inter
communication between programs
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Assembler/Session 1
REGISTERS
Objectives
General purpose registers:
* 16 registers available
* Numbered 0 - 15
* Holds 32 bits (4 bytes) of data (1 Full word)
Floating point registers:
* 4 registers available
* Numbered 0,2,4,6
* Holds 64 bits (8 bytes) of data
Note : The registers 0, 1, 13, 14 and 15 are reserved for special purpose
By IBM convention these registers are used for calling
subprograms
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Assembler/Session 1
DATA REPRESENTATION
Objectives
Binary fields
- Always fixed in length, either 2 or 4 bytes
(Full word or Half word)
- Negative numbers stored in 2’s complement form
Examples:
A
DC
H’295’
01 27
B
H’-75’
FF 35
DC
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Assembler/Session 1
2’s complement form
Objectives
How to identify a negative number?
- Leading bit contains a 1 (In Hex 8 to F)
How to convert to a negative number?
-First switch the bits (1 to 0 , 0 to 1)
-Finally add 1
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Assembler/Session 1
Boundary requirements
Objectives
Full word – Should begin in a full word boundary
(Achieved by aligning with 0F)
Half word – Should begin in a half word boundary
(Achieved by aligning with 0H)
How to find:
The starting address of Full word should end with
0, 4, 8 or C and Half words should end with 0, 2, 4,
6, 8, A, C or E
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Assembler/Session 1
DATA REPRESENTATION
Objectives
Characters
- One byte (EBCDIC form)
- Character representation of decimal digits is called
Zoned Decimal (first nibble is zone and next is digit)
Zone digit
0-9
+, - , blank
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Zone
+
Blank
Code
C, A,E,F
D, B
F
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Assembler/Session 1
DATA REPRESENTATION
Objectives
Floating Point Numbers
- Always fixed in length, 4, 8 or 16 bytes
(Full word, double word, double double word)
- Left most bit represents sign
(0 - positive; 1 - negative)
- Next 7 bits represent exponent
- Remaining bytes represent the fraction
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Assembler/Session 1
DATA REPRESENTATION
Objectives
Decimal numbers ( Packed Decimal representation)
- Each byte but the rightmost has 2 decimal digits (0-9)
- The right most byte contains a digit in the left half and
a sign indicator in the right
Sign indicator: C- Positive
D - Negative
Example: 753
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753C
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Assembler/Session 1
Objectives
Addressing Operands
• Register addressing
• Base, displacement addressing
• Base, index and displacement addressing
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Assembler/Session 1
INSTRUCTION FORMATS
Objectives
RR
opcode R1 R2
SI
opcode
I2
B1
D1
SS
opcode
L
B1
D1
B2
D2
SS
opcode L1 L2 B1
D1
B2
D2
RX
opcode R1 X2 B2
D2
RS
opcode R1 R3 B2
D2
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Assembler/Session 1
Addressing RX Operands:
Objectives
Implicit format:
L 3,VAR
Explicit format:
L 3,100(0,12)
Register Displacement Index reg Base reg
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Assembler/Session 2
Assembler Language
SESSION 2
Addressing
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Assembler/Session 2
STORAGE DEFINITIONS
Objectives
Two ways to define fields :
1. Define a field and initialize the data in it using
the DC assembler directive
2. Define a field without initializing using the DS
assembler directive
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Assembler/Session 2
STORAGE DEFINITIONS
Objectives
Format:
label {DS/DC} dtLn’value’
where :
label
d
t
Ln
: Label used to name the field (optional)
: Duplication factor (optional)
: Type of data ( required)
: The letter ‘L’ followed by the length of the field in
bytes (optional)
value : Represents the value enclosed in apostrophes
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STORAGE DEFINITIONS
Objectives
Examples:
ALPHA
FLDS
H1
F2
F1
F3
DC
DS
DC
DC
DC
DC
C’ABC EF’
3CL2
H’29’
F’-10’
X’03’
PL4’-72’
Note : for character constants truncation or padding is to
the right and for almost all others it is to the left.
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Assembler/Session 2
STORAGE DEFINITIONS
Objectives
DC TYPES
Type
C
X
B
F
H
E
D
L
P
Implied
Length
4
2
4
8
16
-
CTS-PAC
Alignment
Data Representation
None
None
None
Full word
Half word
Full word
Double word
Double word
Character
Hex digits
Binary digits
Binary
Binary
Floating point
Floating point
Floating point
None
Packed decimal
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Assembler/Session 2
STORAGE DEFINITIONS
Objectives
Data Representation in other languages:
Assembler FORTRAN
Language
DC Type
C
Character
F, H
Integer
E
Real
D
X, B
P
CTS-PAC
Double
Precision
Logical
N/A
COBOL
PASCAL
Display
COMP
COMP-1
String
Integer
Real
COMP-2
Real
N/A
COMP-3
Version 2.0
Boolean
N/A
BASIC
String
Integer
Single
precision
Double
Precision
Hex
N/A
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Assembler/Session 2
STORAGE DEFINITIONS
Objectives
Literals
• A literal is a constant preceded by an equals sign ‘=‘.
• Can be used as a main-storage operand but not as a
destination field of an instruction
• Causes assembler to define a field that is initialized with
the data specified
• All constants defined by literals are put by the assembler
in a literal pool, usually at the very end of the program
(Unless changed by LTORG instruction)
L
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R4,=F’1’
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Assembler/Session 2
Objectives
Exercise 1 Q 1 and Q2.
2.What will happen in the following cases
DC CL5’123’
DC CL5’123456’
DC X’A1245’
DC XL2’A1245’
DC XL5’A1245’
DC F’19’
DC FL1’513’
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Assembler/Session 2
Objectives
EQU (Assembler directive)
• The EQU statement is used to associate a
fixed value with a symbol
R4
EQU 4
DRBACK EQU OUT+25
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Assembler/Session 2
ESTABLISHING ADDRESSABILITY
Objectives
• By establishing the addressability of a
coding section, you can refer to the
symbolic addresses defined in it in the
operands of machine instruction
• Assembler will convert the implicit
addresses
into explicit addresses
(base - displacement form)
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Assembler/Session 2
ESTABLISHING ADDRESSABILITY
Objectives
To establish the address of a coding section :
• Specify a base address from which the
assembler can compute displacements
• Assign a base register to contain this base
address
• Write the instruction that loads the base
register with the base address
Note: The base address should remain in the base
register throughout the execution of the program
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Assembler/Session 2
ESTABLISHING ADDRESSABILITY
Objectives
Establishing Base Register
The USING and DROP assembler instructions
enable one to use expressions representing
implicit addresses as operands of machine
instruction statements, leaving the assignment of
base registers and the calculation of
displacements to the assembler
USING - Use Base Address Register
- allows one to specify a base address and assign
one or more base registers
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Assembler/Session 2
ESTABLISHING ADDRESSABILITY
Objectives
To use the USING instruction correctly, one should know :
• which locations in a coding section are made addressable
by the USING statement
• where in a source module you can use these established
addresses as implicit addresses in instruction operands
Format:
symbol USING base address,basereg1| basereg2|,..
e.g.
USING BASE,9,10,11
USING *,12
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Assembler/Session 2
ESTABLISHING ADDRESSABILITY
Objectives
Range of a USING instruction:
• The range of a USING instruction is the 4096
bytes beginning at the base address specified in
the USING instruction
Domain of a USING instruction
• The domain of a USING instruction begins
where the USING instruction appears in a source
module to the end of the source module
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Assembler/Session 2
ESTABLISHING ADDRESSABILITY
Objectives
The assembler converts implicit address references into their
explicit form:
• if the address reference appears in the domain of a
USING instruction
• if the addresses referred to lie within the range of the
same USING instruction
Guideline:
• Specify all USING instructions at the beginning of the
source module
• Specify a base address in each USING instruction that lies
at the beginning of each control section
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Assembler/Session 2
RELATIVE ADDRESSING
Objectives
• Relative addressing is the technique of addressing
instructions and data areas by designating their location
in relation to the location counter or to some symbolic
location
ALPHA
BETA
LR
CR
BCR
AR
3,4
4,6
1,14
2,3
ALPHA+2 or BETA-4
Note : Always avoid using relative addressing
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Assembler/Session 3 & 4
Assembler Language
SESSION 3 & 4
Machine Instructions
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Assembler/Session 3 & 4
HANDLING CHARACTER DATA
Objectives
Move Character Instruction (MVC)
• Copy data from one place in memory to another
Format :
MVC operand1,operand2
S1(L), S2
- implicit
D1(L,B1),D2(B2)
- explicit
e.g...
MVC
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INPUT(5),OUTPUT
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Assembler/Session 3 & 4
HANDLING CHARACTER DATA
Objectives
Move Immediate Instruction (MVI)
• Can move only one byte of constant data to a field
Format : MVI operand1,operand2
S1,I2
- implicit
D1(B1),I2
- explicit
e.g..
MVI
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CTL,C’B’
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Assembler/Session 3 & 4
HANDLING CHARACTER DATA
Objectives
Advanced Techniques
1. Explicit lengths and relative addressing
PAD
MVC
PAD+6(4),=CL4’ ‘
DS
CL10
2. Overlapping fields and the MVC instruction
MVC
FLDB,FLDA
FLDA DC
C’A’
FLDB DS
CL3
Limitation of MVC : Can only move 256 bytes
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Assembler/Session 3 & 4
HANDLING CHARACTER DATA
Objectives
Moving more than 256 characters: MVCL instruction
Uses 2 pairs of even-odd pair of registers
Format : MVCL R1,R2 (Both are even registers)
Reg R1 – Address of destination R1+1 – Length
Reg R2 - Source R2+1 – Padding character (1st 8 bits) and Length
Eg: LA 2,Q
LA 3,2000
LA 4,P
LA 5,1500
MVCL 2,4
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Assembler/Session 3 & 4
HANDLING CHARACTER DATA
Objectives
Comparison Instructions
• Compares 2 values - the values are found in fields, in
registers or in immediate data
CLC - Compare logical character
e.g.
CLC FLDA,FLDB
CLI - Compare logical immediate
e.g.
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CLI
FLDA,C’K’
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Assembler/Session 3 & 4
Objectives
Exercise 2 Q1 and Q2
2. What will be the effect of the following instructions :
MVI OUTAREA,C’ ‘
MVC OUTAREA+1(132),OUTAREA
OUTAREA
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DS
133C
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Assembler/Session 3 & 4
BINARY INSTRUCTIONS
Objectives
Three types of binary instructions
•Full word
•Half word
•Register
The Binary Move Instructions
L, LH, LR ,ST, STH
Type : R,X Register and indexed storage
e.g...
L
5,FULL
LR
5,7
STH 7,HALF
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Assembler/Session 3 & 4
BINARY INSTRUCTIONS
Objectives
Note : Do not mix up the instruction types and field types
e.g.
RES
LH
5,FULL - right half of Reg 5 gets 1st 2 bytes at FULL
L
6,HALF - Reg 6 gets 4 bytes starting from HALF
ST
3,RES
DS
H
HALF DC
H’15’
FULL
F’8’
DC
CTS-PAC
- 4 bytes of reg 3 are stored starting from RES
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Assembler/Session 3 & 4
BINARY INSTRUCTIONS
Objectives
Binary Addition (A, AH and AR)
• Fixed-point overflow occurs when the sum will not
fit in the receiving register
• Type R-X
e.g.
A
5,FULL
AH
6,HALF
AR
7,3
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Assembler/Session 3 & 4
BINARY INSTRUCTIONS
Objectives
Binary Subtraction (S, SH and SR)
• Type R-X
e.g.
S
5,FULL
SH
6,HALF
SR
7,3
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Assembler/Session 3 & 4
BINARY INSTRUCTIONS
Objectives
Binary comparisons (C, CH and CR)
e.g.
C
5,FULL
CH
6,HALF
CR
7,3
Condition code set as HIGH, LOW or EQUAL
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Assembler/Session 3 & 4
Objectives
Binary Multiplication (M, MR, MH)
Format :
M
op1,op2
op1 : An even numbered register; refers to an even-odd
pair of registers
(any register in case of half word format)
op2 : storage area (full word/half word/register)
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Binary Multiplication (M, MR, MH) ...
Function : The value in OP2 is multiplied by the
value in the odd register of the even-odd pair and the result
placed in even-odd registers
(For half word format : The half word specified in OP2 is
multiplied by the value in OP1 and result stored in OP1.)
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Assembler/Session 3 & 4
BINARY INSTRUCTIONS
Objectives
Binary Division (D, DR)
Format:
D
Type
R-X / R-R
:
op1,op2
Op1 : An even numbered register. It refers to an even-odd pair
of registers. The pair holds the double word to be
divided. The even register receives the remainder; the
odd register receives the quotient.
e.g.
D
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4,FULL
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Assembler/Session 3 & 4
BC and BCR Instructions
•
Objectives
instructions that do or do not branch depending on
the value of the condition code
Format
:
BC
M1,S2
BCR M1,R2
e.g.
BC
B’1001’,BRPTA
will cause a branch to the instruction named
BRPTA, if at the time the instruction is executed,
the condition code is 0 or 3.
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Assembler/Session 3 & 4
BRANCHING
Objectives
A branch causes execution to continue at some
other instruction in the program
• Branch conditions : Arithmatic B, BZ,BP,BM,
BNZ,BNP,BNM,BO,BNO
• Comparison BH, BL, BE, BNH, BNL,BNE
e.g : CLI FLDA,C’K’
BNL GOOD
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Assembler/Session 3 & 4
CONDITION CODE PROCESSING
Objectives
•
•
•
condition code occupies 2 bits of PSW
condition code is set by each of a number of instructions
condition code is an extremely important intermediary
between arithmetic instructions and conditional branch
instructions
• very important in implementing control structures
CC Arithmetic
Comparison
0
Zero
First operand = Second operand
1
< Zero
First operand < Second operand
2
>Zero
First operand > second operand
3
Overflow
Not set
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Assembler/Session 3 & 4
LPR, LNR and LCR Instructions
Format:
Objectives
LPR,LNR or LCR R1,R2
LPR - Load positive register (Loads into R1 the
absolute value of R2)
LNR Load Negative register (Loads into R1 the
negative of absolute value of R2)
LCR Load complement register (Loads opposite sign
of the value in R2)
Note: R1 and R2 can be the same
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Assembler/Session 3 & 4
BIT MANIPULATIONS
Objectives
Operation
S-I
S-S
R-R
R-X
OR
OI
OC
OR
O
AND
NI
NC
NR
N
Exclusive OR XI
XC
XR
X
e.g...
OI
FLDA,X’0F’
NR
5,7
X
9,FULL
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Assembler/Session 3 & 4
BIT MANIPULATIONS
Objectives
OR Second 0
First 0
1
1
0
AND
1
1
1
Second 0 1
First 0
0 0
1
0 1
Exclusive OR
Second
CTS-PAC
0
1
First 0
0
1
1
1
0
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Assembler/Session 3 & 4
BIT MANIPULATIONS
Objectives
Testing individual bits - Test under mask (TM)
TM
S1,I2
Function : The bits of S1 ( a single byte) are tested
under the control of the mask in I2 and condition
code is set as ‘all zeroes’, all ones’ or ‘mixed’
e.g.
TM
EMP,B’00000101’
BNM NEXT
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Assembler/Session 3 & 4
BIT MANIPULATIONS
Objectives
Bit Shifting Instructions
SLL, SLDL
Left logical
SRL, SRDL Right logical
(No condition code set)
SLA, SLDA Left arithmetic
SRA, SRDA Right arithmetic
(Sign bit not affected and condition code set)
e.g.
CTS-PAC
SLL
5,1
SRDA
4,5
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Assembler/Session 3 & 4
BIT MANIPULATIONS
Objectives
Bit Shifting Instructions
Condition code setting for arithmetic shift
instructions
0- Result is zero
1- Result is negative
2- Result is positive
3- Overflow generated
Overflow is generated when a bit other than the sign
bit is shifted out
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Assembler/Session 3 & 4
BIT MANIPULATIONS
Translations
•
Objectives
To translate from one bit combination to another
Format :
TR
S1(L),S2 or S1,S2
S1 : The field whose data is to be translated
S2 : A 256-byte translation table
Function : The value of the original byte is used as a
displacement into the translation table. The byte found there
replaces the original byte.
e.g.
TR
WORK,XTABLE
If the source byte is x’40’ (Space), then the displacement into
the table is 64. The value in the table at displacement 64 will
be replacing the source.
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Assembler/Session 3 & 4
BIT MANIPULATIONS
Translations
Objectives
1 byte - 256 possible combinations
x’00’,x’01’, x’02’, x’03’,…………..x’0F’
x’10’,x’11’,x’12’,…………………..x’1F’
…………………………………………..
x’F1’,x’F2’,x’F3’,…………………x’FF’
The table should start with replacement byte for
x’00’ and end with replacement for x’FF’
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Assembler/Session 3 & 4
BIT MANIPULATIONS (TRT)
Objectives
Translations - TRT
(Translate and test register)
-Similar to TR but the source is not changed
-Table is searched similar to TR taking the displacement
into the table
-Usually employed for editing purposes
-The characters we need to search will have non zeros
(x’00’) but other characters will be x’00’.
-Source is searched one character at a time from left to
right
-The first nonzero match in the table halts the
instruction
-Condition code is set to 1 if match found before last
byte, 2 if found at the last and 0 if not found
-Loads address of source operand if found in last 24 bits
of register 1, value from the table into last bit of register
2. No bits are changed in both the registers
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Assembler/Session 3 & 4
BIT MANIPULATIONS (TRT continued)
Objectives
Translations - TRT (Translate and test register)
This example searches for a period X’4B’
The period 4B is decimal 75. So the X’4B’ is placed at the
76th position in the table. (Any non zero character may
be placed in the table
Table should be declared as follows:
TABLE DC 75X’00’
DC
X’4B’
DC 180X’00’
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Assembler/Session 3 & 4
Numeric Conversions
Objectives
1. Conversion to binary (CVB)
Format: CVB operand1,operand2
operand1 : Register
operand2 : a double word (containing
valid packed decimal number)
e.g.
CVB
5,DOUBLE
Use : Character data -(PACK)->Packed decimal-(CVB)->
binary
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Numeric Conversions
Objectives
2. Conversion from binary (CVD)
Format:
CVD operand1,operand2
operand1 : Register
operand2 : a double word
e.g.
CVD 5,DOUBLE
Use : Binary-(CVD)->Packed decimal-(UNPK)->
Character data
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Numeric Conversions
Objectives
3. Conversion from Zoned decimal to packed
(PACK) (SS instruction)
Format:
PACK
operand1,operand2
operand1 : Packed decimal
operand2 : Zoned Decimal
e.g.
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PACK PACKED(3),ZONED(5)
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Numeric Conversions
Objectives
4 Packed decimal to Zoned decimal (UNPACK)
Format:
UNPACK operand1,operand2
operand1 : Zoned decimal
operand2 : Packed decimal
e.g.
CTS-PAC
UNPACK ZD(5),PACKED(2)
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Assembler/Session 3 & 4
Relation between CVD,CVB,PACK and UNPACK
Objectives
PACK
CVB
Binary in
Register
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CVD
Packed
Decimal
Version 2.0
UNPK
Input
Zoned
Decimal
Output
72
Assembler/Session 3 & 4
Example code for Different conversions
Objectives
PACK
PNUM(8),START(3)
CVB
7,PNUM
A
7,=F’1’
CVD
7,PNUM
UNPK
ANS(3),PNUM(8)
…
…
START
DC C’125’
ANS
DS CL3
PNUM
DS
CTS-PAC
D
Version 2.0
73
Assembler/Session 3 & 4
Packed decimal operations
Objectives
SS format - OPCODE D1(L1,B1),D2(L2,B2)
AP - Add packed
SP - Subtract packed
ZAP - Zero and add packed
MP - Multiply packed
DP - Divide packed
CP - Compare packed
Note: All these operations ignore the decimal places. You have to track the
decimal places and edit it with ED and EDMK instructions
CTS-PAC
Version 2.0
74
Assembler/Session 3 & 4
Packed decimal operations
Objectives
Advanced instructions:
SRP - Shift and Round packed OPCODE D1(L,B1),D2(B2),I3
First operand - Memory location including length
Second operand - Direction and number of places to shift
Third operand - Whether to round or not
------------------------------------------------------------------------Second operand, <= 32, left shift is done and 33 to 64 right shift is done.
Number for right shift = ( 64 - number of digits to be shifted)
(No rounding is involved in left shift
CTS-PAC
Version 2.0
75
Assembler/Session 3 & 4
Packed decimal operations
Objectives
Advanced instructions: (SRP continued)
NUM is a 5 byte packed decimal number and contains 001234567C.
What is the value in number after each of these instructions?
1. SRP NUM(5),2,0
2. SRP NUM(5),62,0
3. SRP NUM(5),62,5
4. SRP NUM(5),60,5
CTS-PAC
Version 2.0
76
Assembler/Session 3 & 4
Packed decimal operations
Objectives
Advanced instructions:
MVZ - Move Zone (Moves the first half of each byte)
MVN - Move numeric (Moves the second half of each byte)
MVO - Move with offset
EG: Multiply A by 100 where value of A is 123
MVC TEMP(3),A
MVN TEMP+2(1),=X’00’
MVZ TEMP+3(1),=X’00’
MVN TEMP+3(1),A+2
A
DC PL3’123’
TEMP DS PL4
CTS-PAC
Version 2.0
77
Assembler/Session 3 & 4
Editing the output for printing
Objectives
ED and EDMK instructions ( D1(L,B1), D2(B2)) (Pattern and PD number)
…
Patterns:
… selector
x’20’ - Digit
x’21’ - Significance selector
x’22’ - Field separator
x’60’ - Sign indicator
Pattern and the packed decimal number processed from left 1 byte at a time
X 0 1 2 3 4 5 6 C
(Instruction: ED P(12),X)
Fill Character
P 40 20 20 6B 20 21 20 4B 20 20 60 40 (Before execution)
P 40 40 F1 6B F2 F3 F4 4B F5 F6 40 40 (After execution)
number is positive)
CTS-PAC
1 ,
2 3 4 . 5 6 (Last 2 bytes spaces since
Version 2.0
78
Assembler/Session 3 & 4
Editing the output for printing
Objectives
Values being
examined
Pattern
PD digit
byte
When the
Digit
0
significant
selector
indicator is off
1-9
Significanc 0
e starter
1-9
When the
significant
indicator is on
CTS-PAC
Action taken
New pattern
Fill character
digit in
EBCIDIC
Fill character
New state of
SI
Off
On
On
Field
seperator
Any other
byte
Digit
selector
Significanc
e starter
None
digit in
EBCIDIC
Fill character
None
Fill character
Off
0-9
digit in
EBCIDIC
digit in
EBCIDIC
On
Field
seperator
Any other
byte
None
Fill character
Off
None
Pattern byte
not changed
On
0-9
Version 2.0
On
Off
On
79
Assembler/Session 3 & 4
Editing the output for printing
Objectives
-ED and EDMK can detect the difference between significant and non signi
ficant digits ie between leading and non leading zeros
- Significance starter forces all subsequent digits to be considered significant
-When significance indicator is off and detection of a significant digit turns it
on, the address of that significant digit placed in 8-31 of register 1 by EDMK
-EDMK allows a floating currency and/or algebraic sign but ED does not allow
CTS-PAC
Version 2.0
80
Assembler/Session 3 & 4
TABLE PROCESSING
Objectives
A table is a named storage structure consisting of
subunits or entries
e.g.
RATE
DS
6F
L
4,RATE+8
Accessing table elements with indexed storage
operands:
e.g.
LH
9,=F8’
L
5,RATE(9) (9 - index register)
CTS-PAC
Version 2.0
81
Assembler/Session 3 & 4
Multi-purpose branching instructions
Objectives
Convenient when counted repetition structure (table processing) is
needed
• Branch on count (BCT and BCTR)
Format:
BCT op1,op2
(R-X)
Function: First the op1 value is decremented by 1. Second the
branch is taken to the address specified in op2 only if the value in op1
is not 0.
e.g.
REPEAT
LH
9,=H’12’
EQU
*
..
BCT
CTS-PAC
9,REPEAT
Version 2.0
82
Assembler/Session 3 & 4
• Branch on index high and branch on index low or equal (BXH
and BXLE)
Objectives
Format:
BXLE
op1,op2,op3
BXH
op1 : A register known as the index register
op2 : A even-odd pair of registers
Even register - increment register
Odd register - Limit register
op3 : A storage operand. This is the branch address.
CTS-PAC
Version 2.0
83
Assembler/Session 3 & 4
Function : First, the value in the increment
Objectives
register is added to the indexed register. Second,
the branch is taken only when the value in the
index register is ‘lower than or equal to’ / ‘higher
than’ the value in the limit register
Useful when the same register is to be used as the
count and index register
CTS-PAC
Version 2.0
84
Assembler/Session 3 & 4
‘DO UNTIL’ repetitions
BXLE
-
BXH-
‘DO WHILE’ repetitions
e.g...
LH
7,=H’0’
index
LH
2,=H’2’
increment amount
LH
3,=H’18
the limit
Objectives
--REPEAT
...
LH
6,TABLE(7)
...
BXLE 7,2,REPEAT
CTS-PAC
Version 2.0
85
Assembler/Session 3 & 4
Objectives
Load instructions
with additional features
• Load and Test (LTR)
e.g...
LTR 15,15
BNZ ERROR
• Load Address (LA)
LA R1,D2(X2,B2)
CTS-PAC
Version 2.0
86
Assembler/Session 3 & 4
USING EQUATES
Objectives
• To associate a fixed value with a symbol
• Useful for length and relative address calculation
e.g.
TABLE
DS
0H
DC
C’01
DC
C’02’
...
TBLEND
EQU *
TBLSIZE
EQU TBLEND-TABLE
CTS-PAC
Version 2.0
87
Assembler/Session 3 & 4
USING EQUATES
Can be
Objectives
used for the following purposes:
1. To assign single absolute values to symbols.
2. To assign the values of previously defined
symbols or expressions to new symbols, thus
allowing you to use different mnemonics for
different purposes.
3. To compute expressions whose values are
unknown at coding time or difficult to calculate.
The value of the expressions is then assigned to a
symbol.
CTS-PAC
Version 2.0
88
Assembler/Session 5
Assembler Language
SESSION 5
Program Sectioning
CTS-PAC
Version 2.0
89
Assembler/Session 5
Beginning and End of Source Modules
Objectives
• Code a CSECT segment before any
statement that affects the location
counter
• END statement is required as the last
statement in the assembly
CTS-PAC
Version 2.0
90
Assembler/Session 5
CONTROL SECTIONS
Objectives
•A source module can be divided into
one or more control sections
•A control section is the smallest
subdivision of a program that can be
relocated as a unit
CTS-PAC
Version 2.0
91
CONTROL SECTIONS
• At coding time, establish the addressability
of each control section within the source
module, and provide any symbolic linkages
between control sections that lie in different
source modules.
• Initiated by using the START or CSECT
instruction
CTS-PAC
Version 2.0
92
Assembler/Session 5
CONTROL SECTIONS
Objectives
• Any instruction that affects the location
counter, or uses its current value,
establishes the beginning of the first
control section.
CTS-PAC
Version 2.0
93
CONTROL SECTIONS
Format of CSECT:
Name
Operation
Any symbol
CSECT
Operand
Not required
or blank
Note: The end of a control section or portion of a
control section is marked by (a) any instruction that
defines a new or continued control section, or (b) the
END CTS-PAC
instruction.
Version 2.0
94
Assembler/Session 5
DUMMY SECTIONS
Objectives
• A dummy control section is a reference
control section that allows you to describe
the layout of data in a storage area without
actually reserving any virtual storage.
CTS-PAC
Version 2.0
95
DUMMY SECTIONS
• Use the DSECT instruction to initiate a
dummy control section or to indicate its
continuation.
Format of DSECT:
Name
Operation
Any symbol
DSECT
Operand
Not required
or blank
CTS-PAC
Version 2.0
96
Assembler/Session 5
DUMMY SECTIONS
Objectives
To use a dummy section :
• Reserve a storage area for the
unformatted data
• Ensure that this data is loaded into the area
at execution time
Analogy: Cobol copybook
CTS-PAC
Version 2.0
97
DUMMY SECTIONS
• Ensure that the locations of the symbols in
the dummy section actually correspond to
the locations of the data being described
• Establish the addressability of the dummy
section in combination with the storage area
You can then refer to the unformatted data
symbolically by using the symbols defined in the
dummy section.
CTS-PAC
Version 2.0
98
Assembler/Session 5
ASMBLY2
BEGIN
ATYPE
CSECT
BALR
USING
...
Objectives
2,0
*,2
Reg 3 points to data area
LA
USING
CLI
3,INPUT
INAREA,3
INCODE,C'A'
BE
...
MVC
MVC
ATYPE
WORKA,INPUTA
WORKB,INPUTB
..
CTS-PAC
Version 2.0
99
WORKA
DS
CL20
WORKB
DS
CL18
INPUT
DS
CL39
...
INAREA
DSECT
INCODE
DS
CL1
INPUTA
DS
CL20
INPUTB
DS
CL18
...
CTS-PAC
END
Version 2.0
100
Assembler/Session 5
Assembler Directives
Objectives
TITLE : To provide headings for each page of
the assembly listing of the source modules.
EJECT : To stop the printing of the assembler
listing on the current page, and continue the
printing on the next page.
ORG : To reset the location counter
CTS-PAC
Version 2.0
101
Assembler Directives
LTORG : A literal pool is created
immediately after a LTORG instruction or,
if no LTORG instruction is specified, at the
end of the first control section.
PRINT : To control the amount of detail to
be printed in the listing of programs.
PRINT
CTS-PAC
NOGEN / GEN
Version 2.0
102
Assembler/Session 6
Assembler Language
SESSION 6
Writing a complete program
CTS-PAC
Version 2.0
103
Assembler/Session 6
Program Entry and Exit Logic
Objectives
Program entry - Preserve register contents
Program Exit - Restore register contents
Register save area
Always calling program provides a save area
of 18 Full words long used for storage of
registers
Save area address passed through register 13 by
IBM convention
CTS-PAC
Version 2.0
104
Assembler/Session 6
A register save area (18 consecutive full words)
Word
Objectives
Address
Contents
1
SAV
2
SAV+4
Address of calling program’s save area
3
SAV+8
Address of called program’s save area
4
SAV+12
Contents of Register 14
5
SAV+16
Contents of Register 15
6
SAV+20
Contents of Register 0
...
18
SAV+68
CTS-PAC
Contents of Register 12
Version 2.0
105
Assembler/Session 6
Responsibilities of called program
Objectives
Program entry conventions
1.Save contents of registers 0-12,14 & 15 in
calling program’s save area
2.Establish base register
3.Store calling program’s save area in the 2nd
word of its own save area
CTS-PAC
Version 2.0
106
Assembler/Session 6
Program entry conventions (contd..)
Objectives
4. Store the address of its register save area in the
third word of the calling program’s register save area
(The addresses in the 3d word of save area establish
a chain of register save areas. This will be useful in
reading the dump when program crashes).
CTS-PAC
Version 2.0
107
Assembler/Session 6
Responsibilities of called program (contd..)
Program Entry
STM
Objectives
R14,R12,12(R13)
BALR R12,0
USING *,R12
ST
R13,SAVOWN+4 store calling programs save area
LR
R14,R13
LA
...
R13,SAVOWN
ST
R13,8(R14)
CTS-PAC
Reg 13 contains current prog’s SA
Version 2.0
108
Assembler/Session 6
Responsibilities of called program (contd..)
Objectives
Program Exit conventions
1. Restore registers 0-12 and 14
2. Place the address of the save area provided by the
calling program in Reg 13
3. Place a return code in the low order byte of
register 15 if one is required. Otherwise restore
register 15.
CTS-PAC
Version 2.0
109
Assembler/Session 6
Responsibilities of called program (contd..)
Objectives
Program Exit
L
R13,4(R13)
LM R14,R12,12(R13)
BR R14
CTS-PAC
Version 2.0
110
Assembler/Session 6
Responsibilities of calling program
1. Register 13 mustObjectives
contain the address of a register
save area.
2. Register 15 should be set to the beginning address
of the subroutine
L
R15,=V(SUBENTRY)
where SUBENTRY is the entry address (usually the CSECT
name) of the subroutine
CTS-PAC
Version 2.0
111
Assembler/Session 6
Responsibilities of calling program (contd...)
Objectives
3. Register 14 should
have the return address
4. Register 1 should have the address of the parameter
list
A BALR instruction stores the address of the next
instruction in the calling program into register 14 and
transfers control to the called subroutine
BALR R14,R15
CTS-PAC
Version 2.0
112
Assembler/Session 6
Passing parameters to a subroutine
Objectives
• The standard interface
requires that addresses of
parameters be placed in a block of storage, and the
address of the block be loaded into register 1 as the
subroutine is called
• Both input and output parameters are treated the same
way
e.g... ADDS
CTS-PAC
DC
A(T)
DC
A(U)
DC
A(V)
LA
R1,ADDS
Version 2.0
113
Assembler/Session 6
R1
Main storage
Objectives
Addr of parmlist
Parmlist
parm3
Addr of parm1
CTS-PAC
Addr of parm2
parm1
Addr of parm3
parm2
Version 2.0
114
Assembler/Session 6
Called subroutine B may get the second parameter
Objectives
by
L
R3,4(,R1)
L
R8,0(,R3)
CTS-PAC
Version 2.0
115
Assembler/Session 6
Objectives
Registers with special use
R0 : Contains single word output of a
subroutine
R1 : contains the address of an area of
main storage that contains addresses of
parameters
CTS-PAC
Version 2.0
116
Assembler/Session 6
Objectives
Registers with special use (contd...)
R14 : Contains the return address, the address
in the calling routine to which a subroutine
should return control when finished
R15 : contains the address of the entry point in
the subroutine
R13 : contains the address of an area in which
register contents can be stored by a subroutine
CTS-PAC
Version 2.0
117
Assembler/Session 6
The subroutine RANDOM
Objectives
RANDOM
STM
R14,R12,12(R13)
BALR R12,0
USING *,R12
RN
CTS-PAC
L
R7,RN
M
R6,=F’65541’
ST
R7,RN
LR
R0,R7
LM
R1,R12,24(R13)
BR
R14
DC
F’8193’
Version 2.0
118
Assembler/Session 6
Subroutine RDIGIT
RDIGIT
STM
Objectives
R14,R12,12(R13)
BALR
R12,0
USING
*,R12
ST
R13,SAV+4
LA
R13,SAV
...
L
R15,RANDAD
BALR
R14,R15
...
L
R13,SAV+4
LM
R14,R15,12(R13)
LM
R1,R12,24(R13)
BR
R14
SAV
DS
18F
RANDAD DC
A(RANDOM)
CTS-PAC
Version 2.0
119
Assembler/Session 6
Linkage Conventions
Objectives
•Program divided into 2 or more source
modules
•Source module divided into 2 or more control
sections
•For link-editing, a complete object module or
any individual control section of the object
module can be specified
CTS-PAC
Version 2.0
120
Assembler/Session 6
Communicating between program parts
Objectives
• To communicate between 2 or more source
modules, symbolically link them together
• To communicate between 2 or more control
sections within a source module, establish proper
addressability
CTS-PAC
Version 2.0
121
Assembler/Session 6
Establishing symbolic linkage
Objectives
• Identify external symbols in the EXTRN or WXTRN
instruction or the V-type address constant
• provide A-type or V-type address constants to reserve
storage for addresses represented by external symbols
• In the external source modules, identify these symbols
with the ENTRY instruction
(name entry of a START or CSECT instruction is
automatically identified as an entry symbol)
External symbol dictionary
CTS-PAC
Version 2.0
122
Assembler/Session 6
Establishing symbolic linkage (contd...)
e.g.
TABADR
Objectives
program
A
EXTRN
TABLEB
WXTRN
TABLEB
DS
V(TABLEB)
program B
ENTRY
TABLEB
CTS-PAC
DS
TABLEB
...
Version 2.0
123
Assembler/Session 6
Address Constants (A and V)
Objectives
• An address constant is a main storage address contained
in a constant
• A V-type constant is the value of an external symbol - a
relocatable symbol that is external to the current control
section.
Used for branching to locations in other control sections
e.g
L
5,ADCON
ADCON
DC
A(SOMWHERE)
GSUBAD
DC
V(READATA)
CTS-PAC
Version 2.0
124
Assembler/Session 7
Assembler Language
SESSION 7
Assemble and Link Program
CTS-PAC
Version 2.0
125
Assembler/Session 7
Processing of Instructions
Objectives
Assembler ENTRY
Time/
M/C
Activity
instructions.
Code
source m/c
Macro
EXTRN
Instr.
DC,DS
instruc.
Preassembly
Refer to macro
instruc.
Assembly
object code
LKED
Prog fetch
Execution
data area
form data
area in load mod
CTS-PAC
Version 2.0
126
Assembler/Session 7
JCL ‘ parm’ processing
Objectives
EXEC PGM=pgmname,PARM=
When program gets control :
•Register 1 contains the address of a full word
on a full word boundary in program’s address
space
•the high order bit of this full word is set to 1
(this convention is to indicate the last word in a
variable length parameter list)
CTS-PAC
Version 2.0
127
JCL ‘ parm’ processing ...
• Bits 1-31 of the full word contain the
address of a 2-byte length field on a half
word boundary
• The length field contains a binary count
of the no. of bytes in the PARM field
which immediately follows the length
field
CTS-PAC
Version 2.0
128
Assembler/Session 7
COBOL to Assembler
Objectives
CALL asmpgm USING COMM-AREA
PL/I to Assembler
DCL ASMSUB ENTRY OPTIONS(ASSEMBLER)
CHARSTRING CHAR(25);
CALL
ASMSUB(CHARSTRING);
Ref : PL/I Programming Guide, COBOL programming
Guide
CTS-PAC
Version 2.0
129
Assembler/Session 8
Assembler Language
SESSION 8
Macro Language
CTS-PAC
Version 2.0
130
Assembler/Session 8
Macros
Objectives
• Short source routines written and
stored in libraries
•Assembler inserts the source
statements in the program where
the macro appears
CTS-PAC
Version 2.0
131
Macro Definition
Format :
•A header statement
•A prototype
•Model statements
•A trailer statement
CTS-PAC
Version 2.0
132
Assembler/Session 8
Header statement:
Objectives
MACRO
Prototype:
&name
MOVE
&TO,&FROM,&LENGTH
Model statements:
A set of machine and assembler instructions
Trailer statement:
&name
CTS-PAC
MEND
Version 2.0
133
Assembler/Session 8
Macro Instruction:
Objectives
• A statement containing the name of a
macro
• when expanded, the symbolic parameters in
the model statements are replaced by
corresponding parameters from the macro
instructions
• symbolic parameters may be positional or
keyword
CTS-PAC
Version 2.0
134
Macro Instruction ...
MACRO
&LABEL
HALFSWAP &REG,&SV
&LABEL
ST
&REG,&SV
SLL
&REG,8
IC
&REG,&SV
SLL
&REG,8
IC
&REG,&SV+1
MEND
CTS-PAC
Version 2.0
135
Assembler/Session 8
SET Symbols (global or local)
3 types :
Objectives
• arithmetic (SETA)
• binary (SETB)
• character (SETC)
• SET symbols are declared using,
LCLA
LCLB
LCLC
GCLA
GCLB
GCLC
CTS-PAC
Version 2.0
136
Assembler/Session 8
Format:
Label
operation
operands
Objectives
symbol-name
SETA
An expression
SETB
SETC
e.g.
LCLA
&A1
GCLA
&A2
&A1 SETA
1
&A2 SETA
&A1+3
CTS-PAC
Version 2.0
137
Assembler/Session 8
Attributes
Objectives
There are 6 attributes of a symbol or
symbolic parameter :
type, length, scaling, integer, count and
number
System variable symbols
&SYSINDX, &SYSDATE, &SYSTIME, &SYSECT,
&SYSPARM, &SYSLOC
CTS-PAC
Version 2.0
138
Assembler/Session 8
Conditional Assembly
Objectives
The assembler can be made to branch and loop
among assembler language statements using
sequence symbols and the assembler
instructions AIF and AGO
Sequence symbol : Period followed by 1 to 7
alphabets or digits of which the first is a letter
e.g.
.Z23Ab
CTS-PAC
Version 2.0
139
Assembler/Session 8
Format:
Label
Objectives
Operation Operand
seq symbol AGO
or blank
-do-
AIF
seq. symbol
A logical expression
enclosed in parenthesis,
followed by seq symbol
CTS-PAC
Version 2.0
140
A logical expression is composed of one or
more relations or values of SETB symbols
connected by logical connects AND, OR, AND
NOT, OR NOT
A relation consists of 2 arithmetic expressions
or 2 character expressions connected by a
relational operator EQ, NE, LT, LE, GT, GE
CTS-PAC
Version 2.0
141
Assembler/Session 8
e.g.
MACRO
Objectives
PSRCH
&PARAMS,&STRING
GBLB &FOUND
LCLA &I
&FOUND
SETB 0
.LP
AIF
&I
SETA &I+1
&FOUND
SETB (‘&PARAMS(&I)’ EQ ‘&STRING’)
((&I GE N’&PARAMS) OR &FOUND) .E
AGO .LP
.E
MEND
CTS-PAC
Version 2.0
142
Assembler/Session 8
Accessing QSAM files:
Keywords in DCB
parameter:
Objectives
DSORG
PS
RECFM
F,FA,FB,FBA,V,VBA
BLKSIZE
Block length
LRECL
Record Length
DDNAME
Dataset name in JCL
MACRF
Macro
Physical sequential
GM - Get Move GL - Get Locate
PM - Put Move PL - Put locate
Move parameter directly puts the record in the storage area
specified while Locate mode Loads the address of the record in
Register 1
CTS-PAC
Version 2.0
143
Assembler/Session 8
Accessing VSAM files: ACB macro
AM
-
Objectives
VSAM (For documentation)
BUFND - No. of I/O buffers for data control intervals
BUFNI - No. of I/O buffers for index control intervals
BUFSP - Size of an area for data and Index I/O buffers
DDNAME - Filename used in the DD statement. If omitted
refers to the ACB macro name
EXLST - Address to the EXLST macro. Generates a list of
addresses for user routines
MACRF - Types of processing the file will do
CTS-PAC
Version 2.0
144
Assembler/Session 8
Accessing VSAM files: ACB macro (Continued)
EXLST options:
AM
-
Objectives
VSAM
EODAD = (Address, A/N, L) (Load module)
EXCPAD = (Address, A/N, L) (Load module)
JRNAD = (Address, A/N, L) (Load module)
LERAD = (Address, A/N, L) (Load module)
SYNAD = (Address, A/N, L) (Load module)
Active/No, Stored in load module
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Assembler/Session 8
Accessing VSAM files: RPL macro (Request parameter list)
ACB - Address of
the ACB macro
Objectives
AREA - Address of the work area to be used
AREALEN - Length of the work area (Should be large enough
to hold largest record in Move mode and at least 4 bytes in the Locate mode)
RECLEN -Length of the records in the file (For VB you have
to put the length before writing using MODCB)
ARG - Label containing the key for the search (Key for
KSDS, RRN for RRDS and RBA for ESDS)
OPTCD - 5 sets of groups of parameters
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Assembler/Session 8
Accessing VSAM files: RPL macro (Continued)
Options for OPTCD:
Objectives
KEY/CNV/ADR - Access by key,Control interval or
Relative byte address
SEQ/DIR/SKP - Sequential processing,Direct, Skip
sequential
FWD/BWD - Forward sequential processing,Backward
ARD/LRD -Start seq.processing with ARG specified/
Backward processing from the last record
NUP/NSP/UPD - No updating(Next rec not ready),No
updating Next rec ready(DA only), Record updating)
MVE/LOC - Move mode/ Locate mode
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Assembler/Session 8
Accessing VSAM files:
OPEN - Open theObjectives
file
CLOSE - Close the file
GET - Read a record
PUT - Store a record
ERASE - Delete a record
POINT - Position for access
Advanced macros: SHOWCB, TESTCB, MODCB
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Assembler/Session 9
Assembler Language
SESSION 9
Other Topics
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Assembler/Session 8
Objectives
Characteristics of
good assembler program
• has simple, easy to understand logic
• uses mostly simple instructions
• has no relative addressing
• uses subroutines
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Characteristics of good assembler program ...
• uses DSECTs
• has efficient code (LA R10, 4(0,R10 - A R10,=F’4)
• does not abnormally terminate due to user error
• requests and check feedback from macro instructions
• provides meaningful error messages
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Assembler/Session 8
Characteristics of good assembler program
Objectives
(contd..)
• lets the assembler determine lengths
• has opcodes, operand and comments aligned
• contains meaningful comments
• uses meaningful labels
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Assembler/Session 8
Structured Programming
Objectives
• To improve design and understandability of a
program
• made up of building blocks of subroutines
Conventions for general purpose registers
• Base registers
• Link registers
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Assembler/Session 9
The EXecute Instruction
Objectives
• the EX instruction is a R-X type instruction that
directs the execution of an instruction called the
subject instruction, which is addressed by the second
operand
• the subject instruction is in effect a one-instruction
subroutine
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The EXecute Instruction (contd...)
•The subject instruction is modified before execution
(though not altered at its main storage location) : bits
8-15 of the instruction ORed with bits 24-31 of
register R1 to form the second byte of the instruction
actually executed
e.g. Let reg 9 have the length of string to be moved
EX
R9,VARMVC
VARMVC MVC A(0),B
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Assembler/Session 9
DEBUGGING
Objectives
Exceptions and Interrupts
Interrupts that result directly from attempts at invalid
program execution are called program-check
interrupts; identified by a code
Interruption code 1 : Operation
Interruption code 2 : Privileged operation
Interruption code 4 : Protection
Interruption code 5 :Addressing
Interruption code 6 :Specification
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Assembler/Session 9
DEBUGGING
Objectives
Exceptions and Interrupts (contd..)
Interruption code 7 : Data
Interruption code 8 : Fixed-Point Overflow
Interruption code 9 : Fixed-Point Divide
Other Interruption codes ( 3, 10, 11, 12, 13,
14, 15)
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Assembler/Session 9
DEBUGGING
Objectives
Reading dumps
• whenever a program abends an indicative
dump is generated
• The completion code is a code furnished by
the O/S to designate the reason for the
termination of the job step
• In case of program check interruption, the first
2 digits of the completion code is 0C
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DEBUGGING
Reading dumps ...
• Locate the entry point of your program
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Assembler/Session 9
DEBUGGING
Objectives
Reading dumps (contd...)
• The register contents are the contents at the
point of interruption (the instruction that
caused the interrupt is usually the one just
before the interrupt address given)
• use address at interrupt and entry address to
locate the instruction that caused the programcheck interruption
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Assembler/Session 9
DEBUGGING
Objectives
Full and Partial dumps
• //SYSUDUMP DD SYSOUT=A
• SNAP macro
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DEBUGGING
Reading the dump
• SAVE AREA trace
• P/P Storage
• Examine register contents, PSW and listed entry
point to find the portion of program being executed
• Look at main storage dump to determine the data
being used
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Assembler/Session 9
SYSTEM MACROS
Objectives
Data Management Macros
DCB - Construct a data control block
OPEN - Logically connect a dataset
CLOSE - Logically disconnect a dataset
GET - Obtain next logical record (queued access)
PUT access)
Write next logical record (queued
READ - Read a block (basic access)
WRITE
(basic
access)
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Assembler/Session 9
SYSTEM MACROS
Objectives
Supervisor Services Macros
ABEND - Abnormally terminate a task
CALL - Pass control to a control section
GETMAIN - Allocate virtual storage
FREEMAIN - Free virtual storage
LOAD - Bring a load module into virtual storage
RETURN - return control to the calling program
SAVE - Save register contents
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Assembler/Session 9
SYSTEM MACROS
Objectives
Supervisor Services Macros (contd)
SNAP - Dump virtual storage and continue
LINK - Pass control to a Program in
Another load module
WTO - Write to operator
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Assembler/Session 9
SYSTEM MACROS
e.g. File I/O
Objectives
OPEN (INFILE,INPUT)
GET INFILE,RECAREA
PUT
OUTFILE,RECAREA
CLOSE
(INFILE)
INFILE
DCB
DSORG=PS,MACRF=GM,DDNAME=IFILE
OUTFILE
DCB
DSORG=PS,MACRF=PM,DDNAME=OFILE
(RECFM=,LRECL=,BLKSIZE=,)
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Assembler/Session 9
SYSTEM MACROS
Three forms :
Objectives
Standard form : Results in instructions that store
into an inline parameter list and pass control to the
required program
List form : Provides as out-of-line parameter list
Execute form : Provides the executable instructions
required to modify the out-of-line parameter list
and pass control to the required program
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