Embedded Systems Lab Lab 1 Introduction to Microcontrollers Eng. Dalia A. Awad

Transcription

1 Embedded Systems Lab Lab 1 Introduction to Microcontrollers Eng. Dalia A. Awad Objectives To be familiar with microcontrollers, PIC18F4550 microcontroller. Tools PIC18F4550 Microcontroller, MPLAB software, Proteus VSM simulation program. Theory A microcontroller (or MCU) is a computer-on-a-chip. It is a type of microprocessor emphasizing self-sufficiency and cost-effectiveness, in contrast to a general-purpose microprocessor (the kind used in a PC). A microcontroller is a single integrated circuit, commonly with the following features: Central processing unit - ranging from small and simple 4-bit processors to sophisticated 32- or 64-bit processors. Input/output interfaces such as serial ports (UARTs). Other serial communications interfaces like I²C, Serial Peripheral Interface and Controller Area Network for system interconnect. Peripherals such as timers and watchdog. RAM for data storage. ROM, EPROM, EEPROM or Flash memory for program storage. Clock generator-often an oscillator for a quartz timing crystal, resonator or RC circuit. Many include analog-to-digital converters. Microcontroller versus Microprocessor:

2 A microcontroller differs from a microprocessor in many ways. The first and most important difference is its functionality. In order that the microprocessor may be used, other components such as memory must be added to it. Even though the microprocessors are considered to be powerful computing machines, their weak point is that they are not adjusted to communicating to peripheral equipment. On the other hand, the microcontroller is designed to be all of that in one. No other specialized external components are needed for its application because all necessary circuits which otherwise belong to peripherals are already built into it. It saves the time and space needed to design a device. Input/output Ports: In order to make the microcontroller useful, it has to be connected to additional electronics, i.e. peripherals. Each microcontroller has one or more registers (called a port ) connected to the microcontroller pins. Why input/output? Because you can change the pin s function as you wish. For example, suppose you want your device to turn three signal LEDs and simultaneously monitor the logic state of five sensors or push buttons. Some of ports need to be configured so that there are three outputs (connected to the LEDs) and five inputs (connected to sensors). It is simply performed by software, which means that the pin s function can be changed during operation. Usually, each I/O port is under control of another SFR, which means that each bit of that register determines the state of the corresponding microcontroller pin. For example, by writing logic one (1) to one bit of that control register SFR, the appropriate port pin is automatically configured as input. It means that voltage brought to that pin can be read as logic 0 or 1. Otherwise, by writing zero to the SFR, the appropriate port pin is configured as an output. Its voltage (0V or 5V) corresponds to the state of the appropriate bit of the port register. Memory Unit: Memory is part of the microcontroller used for data storage. 1. Read Only Memory (ROM): ROM (Read Only Memory) is used to permanently save the program being executed. The size of a program that can be written depends on the size of this memory.

3 2. Flash memory: The contents of this memory can be written and cleared practically an unlimited number of times, the microcontrollers with Flash ROM are ideal for learning, experimentation and small-scale manufacture. Because of its popularity, the most microcontrollers are manufactured in flash versions today. So, if you are going to buy a microcontroller, the type to look for is definitely flash. 3. Random Access Memory (RAM): Once the power supply is off the contents of RAM (Random Access Memory) is cleared. It is used for temporary storing data and intermediate results created and used during the operation of the microcontroller. Special Function Register In addition to the registers which do not have any special and predetermined function, every microcontroller has a number of registers whose function is predetermined by the manufacturer. Their bits are connected (literally) to internal circuits such as timers, A/D converter, oscillators and others, which mean that they are directly in command of the operation of the microcontroller. 4. Electrically Erasable Programmable ROM (EEPROM): The contents of the EEPROM may be changed during operation (similar to RAM), but remains permanently saved even upon the power supply goes off (similar to ROM). Accordingly, an EEPROM is often used to store values, created during operation, which must be permanently saved. For example, if you design an electronic lock or an alarm, it would be great to enable the user to create and enter a password, but useless

4 if it is lost every time the power supply goes off. The ideal solution is the microcontroller with an embedded EEPROM. Central Processor Unit (CPU): As its name suggests, this is a unit which monitors and controls all processes inside the microcontroller. It consists of several smaller subunits like Instruction Decoder, Arithmetical Logical Unit (ALU) and Accumulator. PIC microcontrollers: PIC microcontrollers designed by Microchip Technology are likely the right choice for you if you are the beginner. Here is why... The real name of this microcontroller is PICmicro (Peripheral Interface Controller), but it is better known as PIC. Its first ancestor was designed in 1975 by General Instruments. This chip called PIC1650 was meant for totally different purposes. About ten years later, by adding EEPROM memory, this circuit was transformed into a real PIC microcontroller. PIC PIC F Microcontroller High Performance RISC CPU. Operating Frequency: DC 48 MHz Linear program memory addressing to 32 Kbytes. Can store up to 16,384 single-word instructions. Linear data memory addressing to 2 Kbytes. 256 bytes EEPROM memory.

5 Five bidirectional I/O Ports: A, B, C, D, E. Three independent Timers/Counters & Watch-dog timer. Serial Communications: o Enhanced USART Module, Supports RS-485, RS-232. o Master Synchronous Serial Port (MSSP): supports SPI and I2C mode. Streaming Parallel Port (SPP). Incorporate a fully featured Universal Serial Bus communications module that is Compliant with the USB Specification Revision 2.0. Compatible 10-bit Analog-to-Digital Converter: 13 input channels. Pin Diagram

6 Lab Exercises: You took enough instructions for using MPLAB & Proteus ISIS programs in the lab. These instructions should make you able to accomplish the following procedure: Part 1 1. Connect the circuit shown in the Figure_1 below on Proteus ISIS program. 2. Write an assembly language program that send 0x8a to port B. 3. Load the (.hex) file to PIC18f4550 microcontroller. 4. Configure PIC18f4550 parameters needed for the simulation by putting Processor clock frequency 8MHz. 5. Simulate the circuit using Proteus ISIS program.

7 Part 2 1. Connect the circuit shown in the Figure_2 below on Proteus ISIS program. 2. Write an assembly language program that inputs data from port D and sends it to port B. 3. Load the (.hex) file to PIC18f4550 microcontroller. 4. Configure PIC18f4550 parameters needed for the simulation by putting Processor clock frequency 8MHz. 5. Simulate the circuit using Proteus ISIS program. Best Wishes Dalia