DLCD (Digital Logic and Computer Design)
Previous Years question Papers
This subject previously known as STLD upto last year. Course of UNIT 1 and UNIT 2 is same, below shared link will provide some idea for the type of questions that can come to exam.
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https://drive.google.com/drive/u/2/folders/1DM9Z8zIqau0DG1MEITFIxtzzK3p4TmRj
Microprocessor & Microcontroller
UNIT 3
Q1. Differentiate memory mapped I/O and I/O mapped I/O?
Memory Mapped I/O: In this, there is only one address space. Address space is defined as all possible addresses that microprocessor can generate. Some addresses are assigned to memories and some to I/O devices. An I/O device is also treated as a memory location and one address is assigned to it. All the data transfer instructions of the microprocessor can be used for both memory as well as I/O device. This technique is suitable for small systems.
I/O Mapped I/O: In this, addresses assigned to memory locations can also be assigned to I/O devices. Since the same address may be assigned to a memory location or an I/O device, the microprocessor must issue a signal to distinguish whether the address on the address bus is for a memory location or an I/O device.
Q2. Explain input and output modes of operation of 8279 in detail.
Input (Keyboard) modes:
1. Scanned Keyboard Mode: This mode allows a key matrix to be interfaced using either encoded or decoded scans. In the encoded scan, an 8 x 8 keyboard or in decoded scan, a 4 x 8 Keyboard can be interfaced. The code of key pressed with SHIFT and CONTROL status is stored into the FIFO RAM.
2. Scanned Sensor Matrix: In this mode, a sensor array can be interfaced with 8279 using either encoder or decoder scans. With encoder scan 8 x 8 sensor matrix or with decoder scan 4 x 8 sensor matrix can be interfaced. The sensor codes are stored in the CPU addressable sensor RAM.
3. Strobed Input: In this mode, if the control line goes low, the data on return lines, is stored in the FIFO byte by byte.
Output (Display) Modes:
1. Display Scan: In this mode, 8279 provides 8 or 16 character multiplexed displays those can be organized as dual 4-bit or single 8-bit display units.
2. Display Entry: The Display data is entered for display either from the right side or from the left side.
Q3. Interface Stepper Motor to 8086 using 8255 and write Assembly Language Program to rotate Stepper Motor in Clockwise direction and in full stepping. Assume that 8255 is interfaced with 8086 in I/O mapped I/O.
Stepper motor is a device used to obtain an accurate position control of rotating shafts. A stepper motor employs rotation of its shaft in terms of steps, rather than continuous rotation as in case of AC or DC motor. To rotate the shaft of the stepper motor, a sequence of pulses is needed to be applied to the windings of the stepper motor, in proper sequence. The numbers of pulses required for complete rotation of the shaft of the stepper motor are equal to the number of internal teeth on its rotor. The stator teeth and the rotor teeth lock with each other to fix a position of the shaft. With a pulse applied to the winding input, the rotor rotates by one teeth position or an angle x. the angle x may be calculated as.
x = 3600 / no. of rotor teeth.
After the rotation of the shaft through angle x, the rotor locks itself with the next tooth in the sequence on the internal surface of the stator. The typical schematic of a typical stepper motor with four windings is as shown below.
The stepper motors have been designed to work with digital circuits. Binary level pulses of 0-5V are required at its winding inputs to obtain the rotation of the shafts. The sequence of the pulses can be decided, depending upon the required motion of the shaft. By suitable sequence of the pulses the motor can be used in three modes of operation.
• One phase ON (medium torque)
• Two phase ON (high torque)
• Half stepping (low torque)
WORKING:-
8255 is interfaced with 8086 in I/O mapped I/O. Port C (PC0, PC1, PC2, and PC3) is used to give pulse sequence to stepper motor. The 8255 provides very less current which will not be able to drive stepper motor coils so each of the winding of a stepper motor needs to be interfaced using high speed switching Darlington transistors with max 1A, 80V rating with heat sink, with the output port of 8255. Output the sequence in correct order to have the desired direction to rotate the motor.
Assembly Language Program to rotate Stepper Motor in Clockwise direction
MODEL SMALL
.STACK 100
.DATA
PORTA EQU FFC0H
PORTB EQU FFC2H
PORTC EQU FFC4H
CWR EQU FFC6H
PHASEC EQU 03H
PHASEB EQU 06H
PHASED EQU 0CH
PHASEA EQU 09H
.CODE
START:
MOV AL,@DATA
MOV DX,CTL
OUT DX,AL
AGAIN:
MOV AL,PHASEC
MOV DX,PORTC
OUT DX,AL
MOV CX,0FFFFH
UP:
LOOP UP
MOV AL,PHASEB
MOV DX,PORTC
OUT DX,AL
MOV CX,0FFFFH
UP1:
LOOP UP1
MOV AL,PHASED
MOV DX,PORTC
OUT DX,AL
MOV CX,0FFFFH
UP2:
LOOP UP2
MOV AL,PHASEA
MOV DX,PORTC
OUT DX,AL
MOV CX,0FFFFH
UP3:
LOOP UP3
JMP AGAIN
INT 03H
END START
Q4. Explain Analog to Digital Converter and Digital to analog Converter with their interfacing with 8086 microprocessor.
Analog to Digital Converter (ADC) 0809: An Analog-Digital Converter (ADC) is a widely used electronic component that converts an analog electric signal (usually a voltage) into a digital representation. The ADCs are at the front-end of any digital circuit that needs to process signals coming from the exterior world. The ADC0808, ADC0809 data acquisition component is a monolithic CMOS device with an 8-bit analog-to-digital converter, 8-channel multiplexer and microprocessor compatible control logic. The 8-bit A/D converter uses successive approximation as the conversion technique. The converter features a high impedance chopper stabilized comparator, a 256R voltage divider with analog switch tree and a successive approximation register. The 8-channel multiplexer can directly access any of 8-single-ended analog signals. The device eliminates the need for external zero and full-scale adjustments. Easy interfacing to microprocessors is provided by the latched and decoded multiplexer address inputs and latched TTL TRI-STATE outputs.
Features –
Easy interface to all microprocessors
Operates ratio metrically or with 5 VDC or analog span adjusted voltage reference
No zero or full-scale adjust required
8-channel multiplexer with address logic
0V to 5V input range with single 5V power supply
Outputs meet TTL voltage level specifications
ADC0808 equivalent to MM74C949
ADC0809 equivalent to MM74C949-1
ADDRESS LINE A, B, C
The device contains 8-channels. A particular channel is selected by using the address decoder line. The TABLE 1 shows the input states for address lines to select any channel.
Digital to Analog Converter (DAC) 0808:
A Digital to Analog Converter (DAC) converts a digital input signal into an analog output signal. The digital signal is represented with a binary code, which is a combination of bits 0 and 1.
Reference for Programming-----
