Logic shift left
Problem 1. (22 points) Short questions.
1. Which of the following choice(s) is/are correct? A penalty will be applied for every wrong answer.
(a) (4 pts) All sequential circuits can be implemented using
only JK flip-flops and NOT gates
only T flip-flops and NAND gates
only D flip-flops and AND gates
only D flip-flops and NAND gates
(b) (4 pts) An overflow can occur after
the subtraction of two signed numbers
the addition of two unsigned numbers
a logic shift left
an arithmetic shift right
2. Perform the following conversions.
(a) (2 pts) (AB.2AD)16 = ( 171.1672 )10
(b) (2 pts) (10010.0)2 = ( 20 ) 9
3. A digital computer represents its floating point numbers using a signed 6-bit exponent and a signed
normalized 10-bit mantissa. Negative exponent and mantissa values are expressed in 2’s
complement. Show the binary values of the exponent and mantissa to represent (21.1)8.
10-bit mantissa= – —‘0100010010—–
6-bit exponent= _..00101
4. Using Table 6, translate the following machine codes to their equivalent assembly instructions.
Machine code (in Hex.) Equivalent in assembly
ecce BUN CCC I
1234 ADD 234
DCBA BSA CBA I
7002 SZE
lOM oARc PSD|7278690
Problem 2. (20 points) A JK flip-flop A is used by a CPU to perform the following micro-operations
(in RTL):
xT1 :A 0 Reset A to 0
yT2: A 1 Set A to 1
vT3: A 1 Set A to 1
Otherwise the content of A remains the same. The signals T1 , T2, … are outputs of a decoder.
1. Draw the logic diagram of the control circuit governing the flip-flop A.
2. The above micro-operations are replaced by the following ones:
Without using excitation tables and K-maps, draw the new logic diagram of the control circuit
governing the flip-flop A.
Problem 3. (26 points) Consider Program 1.
1. Use Table 6 to translate Program 1 in its equivalent machine code by specifying the machine code of
each instruction/operand (in hexadecimal), and its address in the memory (in hexadecimal)
Program 1: Assembly program
ORG 0
X, HEX 0
ORG 17
Y, LDA A
SZA
LDA B
INC
STA C
HLT
ORG 100
A, 0
B, DEC 14
C, HEX 000A
END
I Address in Hex I Content in Hex I
2. After the execution of the program, what is the content (in hexadecimal) of the word with the symbolic
address C? 0001
3. After the execution of the program, what is the content (in hexadecimal) of the register AC?
AC = 0001
4. After the execution of the program, what is the content (in hexadecimal) of the word with addresszero?
M[0] = 0000
0000 0000
0017 2100
0018 7004
0019 2101
001A 7020
001B 3102
001C 7001
0100 0000
0101 OOOE
0102 OOOA
lOM oARc PSD|7278690
Problem 4. (20 points)
SRT, 0 Solution:
IDA 160
CIR ORG 50
SZE CLA
BUN EXT STA 161
LDA 161 LOP, LDA PTR I
INC STA 160
STA 161 BSA SRT
EXT, BUN SRT l ISZ PTR
ISZ CTR
BUN LOP
HLT
PTR, 100
CTR, FFFO /DEC -16
Problem 5. (36 points) Consider the computer of Lab 3, the architecture of which is described in Figure
1 and Tables 1, 2, 3, 4, and 5. The instruction type is determined by the 2 most significant bits of the 8-
bit register IR, as follows:
• Xo = IR’(7) IR’(6) denotes a memory-referenced instruction (MRI) in direct addressing mode;
• X1 = IR’(7) IR(6) denotes a register-referenced instruction (RRI); and
• X2 = IR(7) IR’(6) denotes a memory-referenced instruction (MRI) in indirect addressing mode.
The flip-flop S is a STOP register which prevents PC from being incremented if S = 1.
Assume that all registers are equipped with 3 control bits for loading the register, increment it by 1, and
reset it to zero.
1. Find the list of all the micro-operations which use the bus and group them according to the register to be
placed on the bus (IR, AR, PC, etc.)
2. Draw the logic diagram of the control circuit which governs the bus.
3. Find the list of all the micro-operation which change: the value of register PC.
” 4. Draw the logic diagram of the control circuit of PC.
