A two-word instruction is stored at location 200 with its address field at locat

Question

A two-word instruction is stored at location 200 with its address field at location 201 (all numbers in hexadecimal). The first word of the instruction specifies the operation code and mode; the second word specifies the address part.
The values of the program counter (PC register), a general register (R1), the index register (XR), the base register (BR), and certain addresses in memory are as shown below.
Evaluate the effective address and the value that is loaded into the AC if the addressing mode of the instruction is:


Addressing Mode Effective address Value of the operand loaded into the AC
a) Immediate
b) Direct addressing
c) Indirect addressing
d) Register
e) Register indirect
f) Relative address
g) Base register addressing
h) Indexed addressing



Memory
Registers Address Content
PC =200 200 Load to AC; Mode
201 Address = 400
R1 = 900 202 Next instruction
: :
XR = 300 300 600
: :
BR = 200 400 300
: :
AC = ? 500 700
: :
600 800
: :
602 802
: :
700 500
: :
800 950
: :
900 850

Explanation / Answer

E.A value in ac a) - | 200// immediate value is taken b) 400 | 300//ea=address provided in instruction c) 300 | 600//ea=[address provided in instruction ] d) - | 900// the value in register e) 900 | 850//ea=[the value in register] f) 600 | 800 //In this mode,the operand is specified as asigned . displacement,relative to PC g) 600 | 800 //ea=br+value in instruction h) 700 | 500//ea=xr+value in istruction

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