Question $1$

The bit masking technique is often used to check whether one or more particular bits in a data

string are OFF. Answer the following questions correctly.

$($a$)$ Explain how the bit masking technique is executed. Give an example in your

explanation.

$(10$ marks$)$

$($b$)$ A block of byte long data residing in between and including the consecutive addresses

$$1000$ to $$4FFF$ are to be used to turn on two LEDs that are individually connected to

two separate output ports of a system designed around the $68000$ microprocessor.

Each data byte has a logic $\text{'}1\text{'}$ for bit $7$ and bit $0$ to turn on the LEDs. However, it is

known that only bits $7$ and $0$ of all of the byte long data set in the memory block is

corrupted. Write an assembly language program for the $68$k that checks the values of

bits $7$ and $0$ of each data byte residing in the memory block in question. The program

must change the value of bit $7$ and $0$ to $\text{'}1\text{'}$ if they are $\text{'}0\text{'},$ resulting in a new data value

that must be restored back at same address position. On the other hand, if bits $7$ and $0$

are already $\text{'}$ I $\text{'},$ the data byte should be retained. The program must also indicate the

number of bit $7$ and $0$ that has been corrected from the data block. The BTST instruction

may not be used in your program.