4. STACK is a LAST- INPUT -FIRST -OUTPUT read/write memory
STACKS is a block of memory that may be used for temporarily storing the
contents of the registers inside the CPU.
The stack is a block of memory locations which is accessed using the
STACK POINTER and STACK SEGMENT registers.
In other words ,it is a a top-bottom data structure whose elements are accessed using
the SP and SS registers.
As we go on storing storing the data words into the stack, the pointer goes on
decrementing and on other hand, pointer goes on incrementing as we go on retriving
the data.
The data in the stack register again may be transferred to stack register whenever is
required by the CPU.
5.
6. PUSH : The process of
storing the data in the
stack is called ’pushing
into’ the stack .
‘
PULL :The process of
transferring of data from
stack to the CPU is called
‘POPPING OFF’
9. INTERRUPT SERVICE ROUTINES
MEANING OF INTERRUPT IS TO MAKE A BREAK IN THE SEQUENCE OF
OPERATIONS.
Interrupt Service Routinees (ISR) are the programs to be executed by
interrupting the main program execution of CPU ,after an interrupt request
appears.
After executing ISR, the control is transferred back again to the main program
which was being executed at the time of interruption .
10.
11.
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13.
14.
15. Definition of the macro
A macro is a group of repetitive instructions in a program which are
codified only once and can be used as many times as necessary.
The main difference between a macro and a procedure is that in the macro the
passage of parameters is possible and in the procedure it is not, this is only
applicable for the TASM - there are other programming languages which do allow it.
At the moment the macro is executed each parameter is substituted by the name or
value specified at the time of the call.
We can say then that a procedure is an extension of a determined
program,while the macro is a module with specific functions which can be used by
different programs.Another difference between a macro and a procedure is the way of
calling each one, to call a procedure the use of a directive is required, on the other
hand the call of macros is done as if it were an assembler instruction.
16. MACROS
.avoid repetitious SAS code
.create generalisable and flexible SAS code
.pass information from one part of a SAS job to another
.conditionally execute data steps and PROCs
.dynamically create code at execution time
