IBM Assembler

Lenght feild is 8 bits so the data is stored in binary

format so if we have all 8 bits set to 1 then the length

will be 128+64+32+16+8+4+2+1 = 255.or

2^7+ 2^6+2^5...2^0 = 255.

so the lenght is 256 .

for example we want to test if given variable is numeric we can do it by following code.

We can define a table with all FF execpt from 0 t0 9 00

Table1 DC 256c'ff'

org table1

dc 10c'00'

Now we can give

TRT var1,table1

BZ numeric

A base register is any general purpose register chosen by

programmer. It is assigned at the beginning of the program

as part of housekeeping with the USING assembler keyword,

and it's purpose is to maintain addressibility within a

page (4k) of code or data.

House keeping is used to store the contents of the base

register from one register to another for using that

register.

These are house keeping instructions where contents of the

registers are stored

1. content of the register 15 is stored in the register 12

2. address in reg 12 is mapped to the module type

3. save area is stored in the register 13

XR Rx,Rx

This is the best way and most efficient way of initializing

the register values or Label values to '0'.

Its because the time required to execute a Logical

Instruction is always less than the Arithmetic Instructions.

e.g SR Rx,Rx consumes more execution time than XR Rx,Rx.

So XR Rx,Rx is a better way to do obtain our target.

In MVS assembler data type X denotes hexadecimal data type

which unsigned pack. suppose you define VAR1 as "VAR1 DC

X'01'". It will occupy 1 byte in the memory and stored as:

0 in the zoned nibble and 1 in the numeric nibble.

P denotes the packed data type, similar to COMP-3 in COBOL.

if you declare any variable with this data type then it

must have a sign byte at last nibble. See following example:

VAR2 DC P'1'

it will occupy one byte in the memory and stored as '1C'.