THEORY EXAMINATION (SEM–VI) 2016-17 MICROCONTROLLERS FOR EMBEDDED SYSTEMS

MICROCONTROLLERS FOR EMBEDDED SYSTEMS (NEC022R)

SECTION – A

(Attempt All | 10 × 2 = 20 Marks)

(a) MOVX and MOVC instructions in 8051

MOVX: Used to transfer data between accumulator and external data memory (RAM).

MOVC: Used to read data from code (program) memory, typically for lookup tables.

(b) Bit addressable RAM in 8051

8051 has 16 bytes (20H–2FH) of RAM that is bit-addressable. Each bit can be accessed individually, making it efficient for flags and control bits.

(c) Pull-up / Pull-down resistor in MSP430

Pull-up resistor: Connects input to logic HIGH when switch is open.

Pull-down resistor: Connects input to logic LOW when switch is open.
In MSP430, these are enabled internally using GPIO registers.

(d) Comparison of 8051 and MSP430x5xxx

(e) Transfer modes in DMA controller of MSP430        Single transfer mode

Block transfer mode                                                     Burst block mode

Repeated single transfer mode                                    Repeated block transfer mode

(f) Data acquisition

Data acquisition is the process of collecting real-world analog signals, converting them into digital form using ADC, and processing them using a microcontroller.

(g) Any four GPIO registers                                         PxDIR – Direction register

PxIN – Input register                                                   PxOUT – Output register

PxREN – Resistor enable register

(h) WDTPW and WDTNMI

WDTPW: Watchdog Timer Password used to enable/disable WDT.

WDTNMI: Configures WDT pin as Non-Maskable Interrupt input.

(i) Serial communication interfaces in MSP430         UART / USART

SPI                                                                              I2C

USCI_Ax and USCI_Bx modules

(j) Features of ADC10 in MSP430                              10-bit resolution

Multiple input channels                                             Low power consumption

Internal reference voltage                                          Sample-and-hold circuit

 SECTION – B

(Attempt Any Five | 5 × 10 = 50 Marks)

(a) Memory-mapped vs I/O-mapped peripherals

Memory-mapped peripherals:                              Share same address space as memory

Accessed using normal load/store instructions

I/O-mapped peripherals:                                       Separate address space

Accessed using special I/O instructions

MSP430 uses memory-mapped peripherals.

(b) Addressing modes in 8051

Immediate                                                                 Direct

Register                                                                     Register indirect

Indexed                                                                     Relative

These modes provide flexibility in data access.

(c) RTC (Real Time Clock) – block diagram & applications

Blocks:                                                                    Oscillator

Counter                                                                    Control registers

Battery backup

Modes:                                                               Clock mode

Calendar mode                                                   Alarm mode

Applications: Digital clocks, data logging, embedded systems.

(d) PWM – working & block diagram

PWM varies duty cycle of a digital signal to control power.

Working:                                                           Timer counts

Compare register sets ON/OFF time                  Duty cycle controls output power

Applications: Motor speed control, LED dimming.

(e) MSP430 program: Toggle LEDs using switch

Logic:                                                                  P1.5 & P1.7 as outputs

P1.2 as input with pull-down                               On switch press → toggle LEDs

(Program written in exam with register-level instructions.)

(f) LED intensity control using PWM                     PWM signal is applied to LED pin.
Increasing duty cycle → more ON time → higher brightness.

(g) Flow chart for receiving single byte via USCI_Bx (I2C)

Steps:                                                                   Configure USCI_Bx

Set slave address = 32H                                      Enable receive mode

Start condition                                                     Receive byte

Stop condition

(h) ZigBee wireless module

ZigBee is a low-power, short-range wireless communication protocol.

Block diagram:                                                 RF transceiver

Microcontroller                                                  Memory

Power unit                                                          Used in IoT, home automation, sensor networks.

SECTION – C

(Attempt Any Two | 2 × 15 = 30 Marks)

(i) 8051 Assembly code to display string on LCD

Steps:                                                                  Initialize LCD

Send command bytes                                         Send ASCII data bytes

Use delay routine                                       (Complete program written in exam-oriented assembly format.)

(ii) Maskable interrupt in MSP430

Maskable interrupts can be enabled or disabled by software.

Working:                                                  Interrupt request generated

CPU checks enable bit                               ISR executed

Return using RETI                                      Used for timers, serial communication, GPIO.

(i) I2C data frame format

Frame includes:                                         Start bit

7-bit slave address                                    R/W bit

ACK/NACK                                                 Data byte

Stop bit                                                      Ensures reliable serial communication.

(ii) GPIO resistors in MSP430x5xx             Pull-up resistor: Input defaults to HIGH

Pull-down resistor: Input defaults to LOW

Enabled using PxREN and PxOUT registers.

(i) Near Field Communication (NFC)

NFC is a short-range wireless technology operating at 13.56 MHz.

Modes:

Reader/Writer mode                                 Peer-to-Peer mode

Card emulation mode                               Used in payments, access cards, smartphones.

(ii) DMA transfer modes                            Single transfer

Block transfer                                             Burst transfer

Repeated transfer modes                          DMA improves performance by reducing CPU load.