1. (30 points) Short Questions:

a.   (3 points) Why 2 instructions are needed to load the timer of the PIT?

f.   (3 points) In Arduino lab #5, why is it                 recommended to hook up the circuit components before connecting the USB cable?

b.   (6 points) What are the 2 approaches to simplify a

Boolean equation derived from a truth table

i)_________________________ and

ii)_________________________

g. (3 points)What is the difference between   combinational logic and sequential logic?

 

c.   (6 points) Name 2 functions of the Programmable Interrupt Controller (PIC)?

 

i)   ___________________________________

 

______________________________________

 

______________________________________

 

ii)  ___________________________________

h. (3 points) Why are there 2 separate L1 cache memories inside a modern CPU chip?

_____________________________________

 

______________________________________

 

d.   (3 points)  Given a certain truth table, there is an unique implementation of it using logic gates.    TRUE: _____            FALSE: ______

 

e.   (3 points) To select data coming from the 32-bit data bus of either an I/O device or a memory       device, how many selector lines (S0, S1, S2,..) are needed?

_____________________

2. (20 points) Combinational Logic:

 

Draw  the  logic  diagram  of a  2-input  exclusive  or (XOR) device using AND, NOT and OR gates.

4. (30 points) I/O Programming:

 

Write an assembly language program xmit to output a buffer of data from the serial port using polling. The  program will exit when it reaches the terminating       character of the buffer. The C prototype for the xmit  function is:

void xmit(int comport, char * buf)

 

where comport is the serial port address and buf is the address of the data buffer

 

3. (20 points) Timer function:

 

In mp4, the slowest interrupt rate that we can program

the PIT is 18 hz. Write a set_timer_count() function

with the correct count value that will generate

interrupts at 36hz.

Answers:

1.   Short Questions

 

a.   The   16-bit  counter  is  made  up  of  two  8-bit registers. You have to load it one at a time.

 

b.   i) Factoring the Boolean equation ii)Karnaugh map

 

c.   i) Mask off interrupt lines

 

ii) Provide the Interrupt vector (IV) to the CPU and the processor uses the IV as an index to the Interrupt Descriptor Table to access the ISR for the device.

d.   FALSE    because    there    are    many    different implementations

 

e.   1 selector line to select one of the two inputs(each input is 32 bits)

 

f.   We   don’t   want   to   damage   the   electronic components due to faulty wiring.

 

Output of sequential logic is a function of its input and previous state.

h.   Instructions   and   data   are   stored   in   different address spaces. Use one L1 cache for instructions and one L1 cache for data.

 

2.   Combinational Logic

Truth Table for XOR:

A   B   Output

0    0    0

0    1    1

1    0    1

1    1    0

 

Boolean equation using sum of products: Output= A#B + AB#

 

 

3. Programming

To calculate the interrupt rate when the counter is loaded with 1, use the following :

There are 65536 downcounts in 1/18 hz= 55ms 1 downcount will take (55x10-3)/65535 sec   The interrupt rate is

1/((55x10-3)/65535) = 1.192 x 106hz

/* Loading a 0 (or 65536) in the counter

results in 18 Hz interrupt rate .

Loading a 32768 in the counter

will interrupt at 36hz

*/

void set_timer_count(void)

{

int count = 32768;

outpt(TIMER_CNTRL_PORT,

TIMER0 |TIMER_SET_ALL |

TIMER_MODE_RATEGEN);

/* set LSB here */                  outpt(TIMER0_COUNT_PORT,count&0xff); /* and MSB here */                  outpt(TIMER0_COUNT_PORT,count>>8);  smalldelay();

/* give the timer a moment to init*/ }

 

4. I/O Programming