Question

Suppose Pep/9 contains the following four hexadecimal values: A: 18BA X: ED20 Mem[001F]: FD03 Mem[0021]: 1A3C If these statements execute continuously, What are the four hexadecimal values after each statement executes ?

(a) C90021

(b) F1001F

(c) 61001F

(d) 990021

Answer 1

Greetings!!

Given machine code represents the following instructions:

(a) C90021 - LDWX 0X0021,D [C9 represent LDWraaa where r=1 represent register X and aaa = 001 represent direct addressing mode. Similarly for all other instructions. Please use manual for getting the opcodes and the corresponding instructions]

(b) F1001F - STBA 0X001F,D

(c) 61001F - ADDA 0X001F,D

(d) 990021 - ORX 0X0021,D

What the instructions do:

LDWX 0X0021,D ;LOAD 0X1A3C WHICH IS STORED AT MEMORY 0Z0021 IS LOADED INTO REGISTER X

STBA 0X001F,D ;STORE THE LOWER BYTE XBA FROM REGISTER A TO THE MEMORY ADDRESS 0X001F

ADDA 0X001F,D ;ADD ACCUMULATOR CONTENT 0X18BA AND MEMORY CONTENT 0XBA03 ie D2BD IN A

ORX 0X0021,D ;OR WITH 0X1A3C AND 0X1A3C ie 0X1A3C IN REGISTER X

After the execution:

A:0XDABD

X:0X1A3C

MEM[001F]:0XBA03

MEM[0021]:0X1A3C

Hope this helps