Question

A BALR instruction appears in a program on line 00C. The instruction itself is 2 bytes long. The next line contains an assembly USING directive. There is a variable called FIELD1 defined at line 2DA.

          (a) What is the displacement that will appear in an instruction which references FIELD1?

          (b)   Assume the BALR instruction reads BALR R10,0. What does this instruction do?

          (c)   What do we call R10?

          (d)   In order to refer to the register as R10, what must you include in your program?

          (e)   Given the above BALR instruction, how would you write the USING directive?

          (f)   What is the purpose of the USING directive?

          (g)   Assume the program is loaded at address 1F34BC.  What will be the address of FIELD1?

Answer 1

2 (a) let us assume that used by given program addressable the locations are byte 00:1 002 BALR, (opcode) ooo BALR2 registe) ood. USING | OO E oof Tolo 730 FIELDI dan ZDA
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tructions at means of USING addressed register : the following instruction statement can be through Rlo as base can be written re) USING directive en two ways. i USING *, Rio 2 here Rio have become base displacement register, at stores the addrers of instruction which is going to be executed next door (1) USING LOORIO here of Rio would have Loc at execution the address - time, NUD 19 ortadatas (4) The main purpose of USING is program addressability It down to generate the object -

Date: machine code, it instructions impacts how are assembled. which base registers and displacements are chosen by assembler when Converting implicit addresses. (g) sf program is loaded at I LF 3 4 BC then addrers FIELDI would be of IF 34 BC + 2DA = (F3796