PART – II
DESCRIPTIVES
Question.1 Describe the operation performed by the instruction OUT 47 h, AL. (3)
Ans : It transfers the content of AL to I/O port 47h. Notice that I/O port number
appears as 0047h on the 16 bit address bus and thatdata from AL appears on the data
bus of the microprocessor.
Question.2 How is 8255 (Programmable Peripheral Interface) configured if its control register
contains 9B h. (3)
Answer
9BH => 1001 1011 =>
b6b5=00-> Mode0
b4=0-> Port A as input.
b3=1-> Port C as input (PC7-PC4)
b2=0-> Mode 0
b1=1-> Port B as input
b0=1-> Port C as input (PC3-PC0).
Question.3 Write a control word for counter 1 of 8253 / 8254that selects the following options:
load least significant byte only, mode 5 of operation and binary counting. Then write
an instruction sequence that will load the control word into 8253 / 8254 that is located
at address 01000 h of memory address space. Assumethat 8253 / 8254 is attached to
the I/O bus of the CPU and the address inputs
0
A and
1
A are supplied by
2
A and
3
A
respectively. (5)
Answer;
Based on the above given conditions and assuming counter 0 is used. The control
word becomes 0001 1010h.
Identify the port address
- The CS is enabled when A7=1
- The Control Register is selected when A1 and A0 =1
- Assuming unused address lines A6 to A2 are at logic 0,
Then port address will be as follows
Control Register = 83H
Counter 2 = 82H
MVI A,B0H
OUT 83H
MVI A, LOWBYTE
OUT 82H
MVI A,HIGHBYTE
OUT 82H
LOOP:MVI A,80H
OUT 83H
IN 82H
MOV D,A
IN 82H
ORA D
JNZ LOOP
RET
Q.4 ‘Pentium processor has a superscalar architecture’. Explain the meaning of the
statement. (4)
Ans
The Pentium microprocessor is organized with three execution units. One executes
floating-point instructions, and the other two (U-pipe and V-pipe) execute integer
instructions. This means that it is possible to execute three instructions
simultaneously.
Q.5 Write a short note on RS-232-C. (8)
Ans
The RS-232 standard is a collection of connectionstandards between different pieces
of equipment. The EIA RS-232 serial communication standard is a universal
standard, originally used to connect teletype terminals to modem devices. In a
modern PC the RS-232 interface is referred to as a COM port. The COM port uses a
9-pin D-type connector (Refer Fig (a)) to attach to the RS-232 cable. The RS-232
standard defines a 25-pin D-type connector (Refer Fig (b)) but IBM reduced this
connector to a 9-pin device so as to reduce cost and size.
AC23 Microprocessor Based System Design
12
Fig (a) Female & Male “DB-9” Connector
Fig 1(b) Female & Male “DB-25” Connector
Question.6
Explain the terms: simplex, half duplex and full duplex. (6)
Answer;
Simplex Transmission
Data in a simplex channel is always one way. Simplex channels are not often used
because it is not possible to send back error or control signals to the transmit end.
An example of a simplex channel in a computer system is the interface between the
keyboard and the computer, in that key codes need only be sent one way from the
keyboard to the computer system.
Half Duplex Transmission
A half duplex channel can send and receive, but notat the same time. It’s like a onelane bridge where two-way traffic must give way in order to cross. Only one end
transmits at a time, the other end receives.
Full Duplex Transmission
Data can travel in both directions simultaneously. There is no need to switch from
transmit to receive mode like in half duplex. It’s like a two lane bridge on a twolane highway.
Q.7 How DRAM’s are different from SRAM’s? Why DRAMs are said to employ
address multiplexing? (4)
Ans
Dynamic RAM (DRAM) is essentially the same as SRAM, except that it retains
data for only 2 or 4 ms on an internal capacitor. After 2 or 4 ms, the contents of the
DRAM must be completely rewritten (refreshed) because the capacitors, which
store logic 1 or logic 0, lose their charges. The entire content of the memory is
refreshed with 256 reads in a 2-to-4 ms interval. Refreshing also occurs during a
write, a read or during a special refresh cycle.
Q.8Explain the operation of 8279. Explain thefollowing terms:
(i) N key Roll over.
(ii) Key board debounce.
(iii) FIFO RAM. (9)
Ans
The 8279 is a programmable keyboard and display interfacing component that
scans and encodes up to a 64-key keyboard and controls up to a 16-digit
numerical display. The keyboard interface has builtin first-in first-out (FIFO)
buffer that allows it store up to eight keystrokes before the microprocessor must
retrieve a character. The display section controls up to 16 numeric displays from
an internal 16 X 8 RAM that stores the coded display information.
The keyboard section consists of eight lines that can be connected to eight
columns of a keyboard, plus two additional lines as well as to shift and
CNTL/STB keys. The key pressed are automatically debounced and the
keyboard can operate in two modes two –key lock outor n-key rollover. If two
keys in the two –key lock out mode are pressed simultaneously, only first key is
recognized. In the N-key roll over mode, simultaneous key are recognized and
their codes are stored in the internal buffer.
Q.9 What are the differences between CGA and VGA graphics adapters? (4)
Ans
The Color Graphics Adapter (CGA), originally also called the Color/Graphics
Adapter or IBM Color/Graphics Monitor Adapter introduced in 1981, was
IBM's first color graphics card, and the first color computer display standard for
the IBM PC.
The standard IBM CGA graphics card was equipped with 16 kilobytes of video
memory, and could be connected either to a NTSC-compatible monitor or TV
via an RCA jack, or to a dedicated 4-bit "RBGI" interface CRT monitor, such as
the IBM 5153 color display.
The term Video Graphics Array (VGA) refers specifically to the display
hardware first introduced with the IBM PS/2 line of computers in 1987, but
through its widespread adoption has also come to mean either an analog
computer display standard, the 15-pin D-subminiature VGA connector or the
640×480 resolution itself. While this resolution has been superseded in the
personal computer market, it is becoming a popular resolution on mobile
devices.
VGA was officially superseded by IBM's XGA standard, but in reality it was
superseded by numerous slightly different extensions to VGA made by clone
manufacturers that came to be known collectively as"Super VGA".
Q.10 What do you mean by A/D conversion? Explain anyone of the following A/D
techniques:
(i) Successive approximation.
(ii) Parallel / flash converter.
(5)
Ans
The electronic circuit, which translates an analogsignal into a digital signal, is
known as Analog - to – Digital converter (ADC).
AC23 Microprocessor Based System Design
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(i) Successive approximation ADC
One method of addressing the digital ramp ADC's shortcomings is the so-called
successive approximation ADC. The only change in this design is a very special
counter circuit known as a successive-approximation register. Instead of
counting up in binary sequence, this register counts by trying all values of bits
starting with the most significant bit and finishing at the least-significant bit.
Throughout the count process, the register monitorsthe comparator's output to
see if the binary count is less than or greater than the analog signal input,
adjusting the bit values accordingly. The way the register counts is identical to
the "trial-and-fit" method of decimal-to-binary conversion, whereby different
values of bits are tried from MSB to LSB to get a binary number that equals the
original decimal number. The advantage to this counting strategy is much faster
results: the DAC output converges on the analog signal input in much larger
steps than with the 0-to-full count sequence of a regular counter.
Without showing the inner workings of the successive-approximation register
(SAR), the circuit looks like this:
Fig: Successive Approximation ADC Circuit
It should be noted that the SAR is generally capable of outputting the binary
number in serial (one bit at a time) format, thus eliminating the need for a shift
register. Plotted over time, the operation of a successive-approximation ADC
looks like this:
Fig: Successive Approximation ADC Circuit Input andoutput Waveforms
ii. Parallel / flash converter.
Also called the parallel A/D converter, this circuit is the simplest to understand.
It is formed of a series of comparators, each one comparing the input signal to a
unique reference voltage. The comparator outputs connect to the inputs of a
priority encoder circuit, which then produces a binary output. The following
illustration shows a 3-bit flash ADC circuit:
Fig: FLASH ADC Circuit
Vref is a stable reference voltage provided by aprecision voltage regulator as
part of the converter circuit, not shown in the schematic. As the analog input
voltage exceeds the reference voltage at each comparator, the comparator
outputs will sequentially saturate to a high state.The priority encoder generates
a binary number based on the highest-order active input, ignoring all other
active inputs.
Q.11 What do you mean by external and internal data bus? How are these two related
in 8088 processor. (2)
AnsInternal Data Bus: A bus that operates only withinthe internal circuitry of
the CPU, communicating among the internal caches ofmemory that are part of
the CPU chip’s design. This bus is typically ratherquick and is independent of
the rest of the computer’s operations.
External Data Bus: A bus that connects a computer to peripheral devices. The
8088 microprocessor has 16-bit registers, 16-bit internal data bus and 20-bit
address bus, which allows the processor address up to 1 MB of memory.
.
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