Question

Give the bit pattern for the instruction LDWX 0x0124,x (pep9)

Answer 1

First 8 bits for LDA instruction will be 1100 raaa.

from them,
First 4 bits,
Instruction specifier for LDA instruction is 1100.

For 5th bit,
if it is accumulator then 1 and if index register then 0.
Here index register X is used. So, r = 1 means 5th bit will be 1.

Other 3 bits(6, 7 and 8) represents addressing mode. x from given instruction specifies Indexed addressing mode.
For index addressing aaa = 101.
Thus,

Fisrt 8 bits will be 1100 1101

Here hexadecimal constant is 0124. Thus other bits are 0000 0001 0010 0100.

Thus, final bit pattern for LDWX 0x0124, x will be
1100 1101 0000 0001 0010 0100.