In this question, you may invent your own instruction set as long as it is reasonable

for your program. You should comment your program properly, so that it can be

easily understood.

$($a$)$ Write an assembly language function to convert an integer $<mn\; id="EditorElement\_3093627">1</mn><mn\; id="EditorElement\_3093628">0</mn><mn\; id="EditorElement\_3093629">0</mn>$ into two single

digit decimal values. For example, if input is $89,$ then output is $8$ and $9,$ and if

input is $3,$ then output is $0$ and $3.$ You can design your calling convention $($i$.$e$.$

where are the input and output parameters for this function. Also, assume there

is NO division operation in the instruction set. No error checking on the input is

needed.$)7$

$($b$)$ Consider a scale with LED display that can measure up to $99g.$ There are two

I$/$O ports, one for reading the weight of the object while the other is

to control two LED displays, each of which can display a single digit from $0$ to

The scale has a Control and Status Register SCSR$,$ and a buffer register SBR$.$

The buffer register is to return the weight of the object.

The SCSR has the following format:

Bit $0$ Ready Bit, the scale is ready

Bit $1$ weight of the object been read and stored in SBR$,$

will be automatically cleared after SBR read

Bit $2$ Set this bit to start reading the scale.

Bit $3$ Scale error

The two LED display is controlled by two LED buffer registers LEDBR$1$ and

LEDBR$2.$ To write to the LED, just write a value between $0$ and $9$ to LEDBR$1$

and LEDBR$2.$ If the value $10$ is written, a hyphen $(-)$ will be displayed.

LEDBR$1-$ the value of the digit to be displayed on the right LED.

LEDBR$2-$ the value of the digit to be displayed on the left LED.

Write an assembly language program that use Programmed $\frac{\text{I}}{O}$ to read the scale

and display the value on the two LEDs. If error is returned from the scale, display

two hyphens $(--).$ You may assume the function in part $($a$)$ is available. $[9]$

$($c$)($i$)$ When does the CPU check interrupt in the instruction execution cycle?

Why? $[3]$

$($ii$)$ What is DMA? Explain how the DMA controller can access the memory

without conflict with the CPU. $[4]$